Curing Color Blindness

If you first learn about your or one of your kids color vision deficiency there is one thing which comes to your mind often just after you learned what it really means to you: Is there a cure for color blindness?

The short answer to this questions is simply: No. And the long answer: There is no cure for color blindness—yet. There are some scientific studies going on which had just recently quite a big breakthrough. This and some other interesting ideas about aids for colorblind people are the topic of this article of the Color Blind Essentials series.

First ideas

“No method had been found for the correction of color blindness [and] any treatment which convinces operators that they can see colors they could not see before will decrease safety in transportation, decrease security in national defense, and decrease efficiency in industry.”
– American Committee on Optics & Visual Physiology

As with many other handicaps or diseases when some people learned that some others can’t really distinguish colors like themselves, laziness was the first thing which came to their mind. Because of that many colorblind people just started to learn color names more intensively—without any success.

There were also some other techniques like warming one eye, electrical stimulation, injections of iodine or extracts of cobra venom, vitamins or flashing light. All this finally resulted in an official statement of different Academies and Medical Associations that no method had been found for the correction of color blindness, whether called ‘color weakness’, ‘color confusion’ or ‘color defectiveness’—which is still true as of today.

But there were also some good ideas around like color filters or spectacles with horizontally divided red and green sections.

Aids for colorblind people

If you have a closer look at the available tools for color deficient people, you have on one side the computer and all its possibilities and on the other side non-computer based aids.

On the non-computer side there is actually just one technique used: colored filters. These filters come in different forms:

  • Lenses: Manufacturers of tinted lenses claim that their product can improve color vision for colorblind users. And people often read this as if they could almost cure your color blindness—which is wrong. Here are some facts about tinted lenses:
    • They have to be worn in only one eye, as otherwise fewer colors are seen.
    • It needs some time to get used to them and learn some new colors.
    • They can help you and enhance your color perception in certain situations.
    • You want be able to see more colors, but maybe other ones then you are used to.
    • Certain colors seem to vibrate or shimmer because of the usage in only one eye.
    • Worn while you are driving they can be a safety risk because of the worse perception at dim light situations.
  • Glasses: It is almost the same for colored glasses as for lenses. The first products looked a bit strange as only one glass is tinted. Recent products have some coating which reduces this effect and makes glasses a true alternative for the lenses.
  • Tools: There is a little tool called Seekey which is made of two tinted filters, one in green and the other in red. If you look through the filters on and off you can definitely distinguish more colors as a colorblind. This can be an advantage for some specific tasks in certain professions or in some everyday life situations. Such filters can also enhance certain diagnostic or medical instruments and help the colorblind operators to see what they otherwise wouldn’t spot that easy.

Many colored filters can help you to pass some color blindness tests, specially the famous Ishihara plates test. But this is not the correct purpose as those tests are usually there to assure, that your color vision isn’t a safety issue. Because of that in most cases tinted filters are not allowed to be used on such qualifying tests.

If we have a look at the computer based helpers for colorblind users, there are different tools available. Those tools make use of different techniques which can only be done digitally.

  • Show the name of a color if you point to it.
  • Shift the whole color spectrum around the color wheel.
  • Highlight certain specific colors in a different color.
  • Use a pattern to highlight certain tints.
  • Some sophisticated algorithms which try to manipulate a picture to the effect that colorblind people perceive it still as normal but that certain shades can be distinguished better.

Such tools might really help you in some specific situations. But often they are not that easy to adapt for your personal purposes and sometimes just to cumbersome to handle. And don’t forget that all those tools can only be used while working on a computer, which is in everyday life often not such a big handicap for colorblind people.

Cure of color vision deficiency

As mentioned in the lead of this article there is to this day no cure for colorblind people available—but it looks like as if there is one for colorblind monkeys!

Monkey Performing Color Blindness Test

Jay Neitz, a well known vision scientist, and his team developed a gene therapy to enhance color vision. Colorblind monkeys were used as test animals. They received the gene injections directly into their eyes to build up the missing color receptor.

The monkeys had to perform a color blindness test and if they did well they received a reward. After a while they started to perform much better on a task they couldn’t accomplish before because of their vision handicap.

Due to this test result many colorblind people hope to be able to get rid of their color vision deficiency in the near future. Unfortunately this won’t come true that fast. And there are some difficulties which have to be overcome until this dream could get true:

  • Gene therapy for red-green color blindness may not work for humans as well as it does for monkeys.
  • Side effects of subretinal injections can include irritation or infection, in addition to the risks of permanent retinal detachment and blindness at the injection site.
  • There could be adverse psychological effects associated with suddenly being able to see new colors and learning how to categorize them.

Also other institutions started to pick up this topic and are looking into the development of such a gene therapy to heal congenital color vision deficiency.

There is a possibility that a color vision handicap can disappear again. In some cases of acquired color blindness, specially for vision deficiencies which can occur after a hard hit on your head, it is reported that this handicap can disappear again after a certain time. Unfortunately this can’t be influenced and the process of healing can’t be used for all other colorblind people.

This was the last part of the Color Blind Essentials series. If you would like to learn more details about color vision deficiency why don’t you browse my articles archive, try some of the color blindness tests or check out my tools including a color blindness simulator.

Living with Color Blindness

“Which color is that?” is an often heard question if you are colorblind. You get used to it. You also learn how to handle it like most other difficulties which arise from your color vision deficiency.

I this article of the Color Blind Essentials series I would like to have a closer look at the every day life of a colorblind person and also at the impacts this vision handicap can have on your career choice.

Color blindness in everyday life

Most people think traffic lights are one of the biggest issue for everyone suffering from a color vision deficiency, but they are wrong. The colors for traffic lights are very well chosen and they are always arranged in a certain order. So this is not a problem at all for most colorblind people even if some states don’t allow you to get a drivers license if you are colorblind.

Bananas Big - Normal
Bananas Big - Deuteranope

Original and its color blind simulation.

But there are some real handicaps for people who are suffering from some moderate to strong color vision deficiency:

  • A Sunburn can’t really be seen, only if the skin is almost glowing.
  • If meat is cooked can’t be told by its color.
  • There is no difference between the colors for vacant (green) and occupied (red).
  • Flowers and fruits can’t be that easily spotted sometimes.
  • And you can’t tell if a fruit or vegetable is ripe or not yet.
  • Every electrical device which uses LED lights to indicate something is a permanent source of annoyance.
  • Colored maps and graphics can sometimes be very hard to decipher.

By far the most biggest issue is matching colors and specially matching clothes.

If you a have a color vision defect you can’t just choose flowers which fit together nicely, or a painting which fits with the furniture, or a carpet. You also can’t create a web site or an image with nicely matching colors. And you will never be able to easily match your shirt with your tie, your trousers with your shoes, your whole wardrobe.

In this case you need a pair of color enabled eyes which help you out. I often borrow the eyes of my wife and sometimes those of my son. They really help me a lot. ;-)

Choosing your career as a colorblind

A color vision deficiency often gets more attention when it comes to choosing a future career. Specially parents are very concerned about possible restrictions. But also young people ask themselves, if the job of their dreams will stay just a dream because of their vision handicap.

Professions that require good to perfect color visionAirline pilot
Air traffic controller
Police officer
Train driver
Some ranks in the armed forces
Some electrical/electronic engineers

Jobs which require good color vision can be split into two different categories. In the first of them color matching or color recognition is a main component of the job. This for example includes color quality control, art teaching, interior decorating and more.

This group of jobs is easy to decide about for colorblind people as each one knows best himself if he will perform well in such a profession or not. Most colorblind people can also accept this fact more or less easily.

The other category includes jobs which also require good color vision but only in support of the job itself. This group includes the job profiles of pilots, firefighters, police officers and more. These kind of jobs have the following facts in common:

  • Bad color vision is a security problem in this job.
  • Passing a color blindness test is required to qualify for the job.
  • The impact of a color vision deficiency is not well described.
  • There is no international standard on color vision requirements.

The points listed above unfortunately make it very complicated. Many colorblind people believe that they still could perform in such a position perfectly and that turning them down just because of their color vision deficiency is not correct. Some people even start thinking about how to cheat on such a test just to get through the exams and get the job of their dreams. But this is not the right way to go.

Here is my six steps plan towards your future career:







(1) Learn. During your time at school learn how you can handle colors. Learn about the severity of your color blindness and learn your special techniques to get around your handicap. This way you are very well prepared when it comes to choosing your future career.

(2) Inform. Get all possible information about the job of your dreams and possible handicaps for color blind people. You can get information from a prospective employer, from special authorities like the FAA for pilot candidates and of course from the internet. It’s important to check your local requirements as they can vary between different countries.

(3) Talk. Try to find some people who are working in this job and talk to them. They will know the best if there are special tasks which might be a problem and you will know from your personal experiences, if you will be able to handle and also most important if you will feel comfortable in such a position. First check your relatives, ask around in your neighborhood, maybe you will find somebody at the college and otherwise I’m sure you will be able to find somebody online who will be happy to help you out. Just check forums where those people could hang around.

(4) Communicate. Don not try to hide your color vision deficiency. Be honest and communicate it if it might be a problem. Of course you only have to do this if color vision could be a possible handicap. But it is important to inform your prospective employer what you learned about the job to be done and how you overcome those handicaps despite your imperfect color vision.

(5) Go for it. Don’t forget to take the last step. Do the required tests to learn more about your color blindness. You might pass without any problem and you might fail. You maybe also like to try different employers as there are in most jobs no national rules concerning color vision deficiency.

(6) Discuss. Did you fail the color blindness test and did they use the Ishihara plates or some similar form? Read the chapter about color blindness tests to learn about other possible tests. This should help you to start a discussion about the used test and if maybe this test was just to restrictive. There are many different tests available and sometimes it would be even much better if your prospective employer would just check possible job restrictions and if you can handle those or not.

And please don’t forget the fact, many people have some form of handicap which is a burden and sometimes becomes a big obstacle. Get used to your color blindness and try to accept that moderate to strong color blind people shouldn’t dream to work for example as a pilot or a professional firefighter. If you can’t accept this, don’t try to cheat on the tests but start a discussion about it!

Red Apple - Normal Red Apple - Protanope

Left: normal red apples — Right: colorblind red apples

We are colorblind. We can’t name colors. But we can handle most situations perfectly even if we don’t know correctly which color it really is.

In the next and last article of the Color Blind Essentials series we will learn if there are any possibilities to cure color blindness.

Photos taken by clairity and Muffet.

5 Questions about Color Blindness

Lily is working on a school project about color vision deficiency. She’s on the way to write a paper about it and has some questions which I would like to answer in this article.

Question 1: What are your feelings on the recent discovery regarding monkeys and a possible cure for their colorblindness? Do you think that it is legitimate, and do you think it should be used on humans in the future?

I think we have to look at this in a broader view. Personally I don’t believe that one of the big problems of our society is to cure color blindness. But scientific work in this area—genetic eye treatments—may help us to understand much better how we can help other people and heal some severe diseases.

And if there is a breakthrough why shouldn’t we use it on humans? Every person should be free to decide if he or she wants such a treatment or not.

Question 2: Do people affected by monochromatism look at life differently? Do they have less emotions because they live in a black and white world?

Yes, definitely. If you are suffering from monochromatism you are not only living in a gray world but also are severely sensitive to light, long sighted and more. This for sure makes your life look different.

Besides that if we only look at the world in gray colors I also think, that this changes a lot. You will see other things as all the colors don’t disturb your perception. Of course you will also not see certain things as the brightness difference might be to small for your eyes. There are certain things which you would struggle with but overall I would say if you are suffering from monochromacy you don’t look at life differently, but just at the world if you have to fulfill and live in a surrounding created by people with color vision.

And I don’t see any relation between emotions and colors because even little babies show a lot of emotions before they really can see colors at all.

Question 3: Should public schools be required to incorporate information about colorblindness in their science curriculum?

No I don’t think so. There are so many interesting scientific things which we can learn at school and color blindness doesn’t need a special treatment in this curriculum.

What I think should be done is to teach the teachers on the topic of color vision deficiency. Every teacher should at least once hear about it and maybe know some techniques to help colorblind students. I strongly believe that every colorblind pupil will find its way through school perfectly and teachers could support this if they sometimes only would know a little more about it.

Question 4: Are there any alternative attempts to cure colorblindness that you are aware of? If so, how affective are they?

There are people who claim, that corrective colored lenses or glasses can cure your color blindness or also some Chinese medicine techniques claim to help. Personally I don’t believe that there are some other possibilities to cure a color vision deficiency.

In 99% of all cases color blindness is encoded in your chromosomes. Therefore you can’t just adjust something easily or push some hidden trigger to cure it.

Question 5: What social disruptions can colorblindness bring upon a person’s life? Teenagers lives in particular. I am colorblind and my mom and sister are both artists. I can not take art class, interior design, yearbook, or any classes like that because of my condition. Can you think of anymore?

Just recently I received an email from a 15 year old boy who is getting teased by his classmates because of his color blindness. So this really can be a problem but I suppose this doesn’t happen to often and is only a problem at a certain age.

Of course, there are certain jobs you can’t accomplish as a colorblind person. Jobs which relate on color vision as their primary task like the ones you mention, or jobs which need good color vision usually for safety reasons. This often causes a lot of frustration among people who realize that they can’t start a career of their dreams, which I fully understand.

But many other people also can’t make their dreams come true. We have two possibilities to follow in this case. Either we work towards better regulations, better aids and tools, and better education in the topic of color vision deficiency. Or we have to accept that not every dream will become true in our lifes.

Color Blindness Tests

Ishihara plate

Ishihara plate

Most people relate the term color blindness test to the dotted pictures or even to the name Ishihara.

But this is not the only one, not the best one, definitely not the most current one, and most often an unsuitable test which is still used all around the world.

This part of the Color Blind Essentials series focuses on the different possibilities to test color vision, how they work, what they can be used for and lists some of the well-known and used tests. There will be no conclusive enumeration as there are just to many tests around, with a lot of them not available anymore but still in use.

First color blindness tests

Already in the 17th century Turberville found differences in some individuals color naming, which was definitely one of the first color blindness tests. About one hundred years later John Dalton described in detail his color vision and also tested other people with some colored ribbons which had to be named as well. At this time most often color vision deficiency was reported simply by subjective descriptions.

In 1837 August Seebeck used some more advanced technique. He used a set of more than 300 colored papers and let people match or find a closely related color to a sample color. This type of color vision test abandoned the naming of colors, which differs a lot between test persons. Through Seebeck’s color blindness test two different types of red-green color blindness and a broad severity scale were discovered. Holmgren adopted this kind of test in 1877 by using skeins of wool. The Holmgren wool test was widely used and even commercially available more than one hundred years later.

The following two developments happened around the same time. They led to modern color vision deficiency testing.

  • John William Strutt Rayleigh developed a precise color matching test. This match—still known as Rayleigh match—is not only the base of modern anomaloscopes but also made him discover dichromatism and anomalous trichromatism.
  • Dr. J. Spilling published the first painted set of pseudoisochromatic plates. They were the predecessors of the famous Ishihara plates, which were produced the first time in 1917.

The different color vision deficiency test forms




The anomaloscope provides the most accurate possibility to test the severity of color blindness and distinguish between dichromats and anomalous trichromats.

It is based on the Rayleigh match: A mixture of red and green light sources has to be matched with a yellow light source. Through the matching range it is possible to discover all different types of red-green color vision deficiency. Some of the anomaloscopes also include the Moreland match (blue-green) to test for tritan defects.

If you are a dichromat you will be able to make a match for all red-green mixture ratios. Anomalous trichromats don’t accept the normal match and the distance of their match indicates the severity of their deficiency. On the other side, if you suffer a protan vision deficiency you will use much more red to match the colors compared to people with a deutan defect, which use more green in their mixture.

In 1907 the Nagel anomaloscope was introduced and is still known as one of the best. Unfortunately it is not produced anymore. Other well known instruments are the Neitz anomaloscope, the HMC (Heidelberg Multi Color) anomaloscope or the Pickford-Nicolson anomaloscope.

Pseudoisochromatic plates

Pseudoisochromatic plates are the most famous type of color blindness test. Most people know them under the name Ishihara plates test, because Dr. Shinobu Ishihara was one of the first persons who designed a very reliable plate test, introduced in 1917. He produced different test sets. Ishihara plates are still widely used all around the world.

The copunctual points build the source for this type of color vision test. The fact that colorblind people can’t distinguish colors along the confusion lines is used to build a pattern of differently colored dots. If you are color blind you won’t spot the dots which are shifted along the confusion lines and therefore numbers, letters, lines or anything else can be hidden from you.

There exist four different type of plates:

  • Vanishing design: Only people with good color vision can see the sign. If you are colorblind you won’t see anything.
  • Transformation design: Color blind people will see a different sign than people with no color vision handicap.
  • Hidden digit design: Only colorblind people are able to spot the sign. If you have perfect color vision, you won’t be able to see it.
  • Classification design: This is used to differentiate between red- and green-blind persons. The vanishing design is used on either side of the plate, one side for deutan defects an the other for protans.

Why can colorblind people see something which is not visible for people with perfect color vision?
If you are colorblind you are not distracted by hue differences along the confusion lines. You will be more focused on lightness differences. This two different facts are used to design the hidden or invisible plates.

Besides the most famous Ishihara plates exists in a standard version of 38 plates, a shorter version of 24 plates and a concise test containing 14 plates. Ishihara plates can only be used to classify red-green color vision deficiencies. Tritan defects can not be evaluated by these tests.

The other well known pseudoisochromatic test plates are the 24 HRR plates by Hardy, Rand and Ritter. This test was first produced in 1954 and can be used the classify all three different forms of color vision deficiency. There also exist a lot more of such tests but none of them is widely used. Even some electronic vision test equipments include certain pseudoisochromatic plates as a quick color vision test. But none of them is very accurate to get a concise test result.

Arrangement tests

Arrangement tests are also based on the theory of copunctual points. In contrast to the static pseudoisochromatic plates where you have to spot a path or number, an arrangement test is dynamic.

D-15 Color Arrangement Test

D-15 Color Arrangement Test

Every such test consists of a certain number of colored discs or plates which have to be arranged in the correct order, starting from a pilot plate. The colors are chosen around the white point and because colorblind people can not distinguish colors along certain lines they will arrange the discs completely different compared to somebody with normal color vision.

The most well known test was introduced by Fransworth in the forties of the last century and is called Farnsworth D-15 arrangement test. As the names suggests this test includes 15 colored plates which have to be arranged in the correct order. You can try an online version of this test right here at Colblindor: Color Arrangement Test.

Some other well known tests in this category are the Lanthony desaturated D-15 test, which is used to classify milder forms of color blindness and the Farnsworth-Munsell 100 hue test. This test includes 100 different plates which have to be arranged in batches of 20 plates. Unfortunately the results are not that better compared to the 15 plates versions.


The last well known type of tests was introduced by railway companies which discovered, that some of their employees couldn’t distinguish certain signal lights. Lantern tests are specially designed to simulate signals and are therefore most often used as vocational tests.

Compared to the other tests with lanterns you are testing the required ability directly. They are robust and have a high practical value. On the other side you can’t reveal much of the nature and severity of the color vision defect.

  • Holmes-Wright lanterns: This lantern includes two different green, two red and a white light. Lights are shown in pairs of two, low or high brightness, either vertically or horizontally aligned. The test person is asked to name the colors.
  • Farnsworth lantern (Falant): This is the standard test in the US. It is comparable to the Holmes-Wright lantern but is specially designed to pass people with a mild form of color vision deficiency.
  • Beyne lantern: France.
  • Giles-Archer lanterns: UK.
  • Edridge-Green lantern: UK.

The following table shows an overview of the different main test types for color blindness and compares them in certain dimensions. Every test type is graded from (-) not capable to (+++) excellent capability.

Comparison of different color vision deficiency test types:
Anomaloscope Plates Arrangement Lanterns
Identifying CVD +++ +++ +
Classifying type +++ ++ ++
Grading severity +++ + ++ +
Classifying dichromat
anomalous trichromat
Occupational suitability +++ +++

Unfortunately Ishihara plates are used much to often to check for occupational suitability. Lanterns or certain arrangement tests would be much better in this case. And if you like to have a precise diagnosis of your color vision deficiency there is no way around an anomaloscope.

The future of color vision testing

Today in our digital world one might think, why don’t we have some simple computer based color blindness test. Unfortunately this is not as simple as it looks like. There are two main problems:

  1. Computers displays just make use of three main colors red, green and blue (RGB). Every other color gets mixed from those three colors. The anomaloscope and lantern tests use different light sources which can’t be simulated by a display.
  2. Every computer display has a different color range it covers, little differences in light sources, different brightness and more. This causes different test results. Only calibrated computers can be used to perform such computer based tests.

The City University in London developed a computer based color vision test which is also based on the same principal as pseudoisochromatic plates and arrangement tests. The main difference is that the colors are constantly changing which gives some really good results. Just recently they used their test to check color vision in pilot candidates and it looks like as the Color Assessment & Diagnosis Test (CAD Test) could become a standard screening instrument for color vision testing. At least for certain professions, where color vision is critical but people with a mild form of color vision still perform perfectly.

There are also some genetic screenings available. But even such a simple impairment as color blindness is not easy to detect in the genes. So every genetic test always needs some physical tests in parallel to get a proper and concise test result.

Color naming would be a very simple test to identify color blindness. But for most cases this is just to simple, to unspecific and not reliable enough. Therefore color naming can be used to check if you have a moderate to strong color vision deficiency but not for a detailed classification of your color vision deficiency.

The next part of the Color Blind Essentials series focuses on how color blindness can affect your everyday life.

Red-Green Color Blindness

You could already learn a lot about the different types of color blindness and what color blindness actually is. In this chapter of Color Blind Essentials I would like to tell and show you some more and deeper details about the most common and also most well known type of color vision deficiency: red-green color blindness.

Discovery of red-green color blindness

Memoirs of the life and scientific
researches of John Dalton

Already John Dalton wrote about his color vision deficiency. Red, orange, yellow, and green all appeared to be the same color to him. The rest of the color spectrum seemed to be blue, gradually changing to purple. Dalton concluded already in the year 1798, that he can not see long wavelength red light—known as protanopia today.

Some recent genetic analysis of Dalton’s preserved eyes showed, that he was suffering from deuteranopia—another form of red-green color blindness. But anyway this is the first description of the red-green color vision deficiency.

In 1837 August Seebeck carried out some systematic color vision tests and found two different classes of red-green color blindness with differences in severity from weak to strong in both classes.

After that investigations started to gather more details and scientists learned a lot more about our color vision: The genetic source of color vision, its deficiencies and the precise knowledge about the mechanism of color vision in our eyes.

The facts

With the knowledge of the last two chapters on what color blindness really is and the different types of color blindness, we can put together the following list of facts about red-green color blindness:

Facts on Red-Green Color Blindness
Red-green color blindness is a generic term for protanopia (red-blindness), protanomaly (red-weakness), deuteranopia (green-blindness), and deuteranomaly (green-weakness).
More than 99% of all color blind people are suffering from a red-green color vision deficiency.
About 8% of all men and 0.5% of all women are suffering from it.
Any severity starting from slightly over moderately, strongly or absolutely is possible.
Red-green color blindness is a recessive, sex linked trait (encoded on the X chromosome). This results in much more men to suffer from it than women.
It is usually inherited from a grandfather to his grandson, with the mother in between acting as the carrier of the disease.
Not only red and green can’t be distinguished, but the whole color spectrum is affected by color blindness.

Unfortunately many people don’t even know one of those seven basic facts on red-green color blindness. This often causes a lot of confusion and many misunderstandings related to this term.

Often confused colors

The following little story happened to me a few years back. I am suffering from a strong red-blindness, so this is really a true story:

I was standing on a balcony with a few friends on the fourth floor, looking into the grass fields down below us. After a while one of my friends asked, why the fire hydrant is standing in the middle of the field with no path close to it.

I looked down and asked: “Which fire hydrant?” — Silence — Laughter.

“Can’t you see that orange fire hydrant in the middle of the field? It stands out so obviously with its orange color!”

I couldn’t see it. Only after a while, scanning the field for a fire hydrant, I found it. But not because of its color but of its structure.

This story is very typical as orange and green are some of the big problem colors for red-green color blind people. But not only those colors are mixed up. Colors from the whole color spectrum can cause problems in terms of not being able to distinguish them if you are color blind.

The table on the left shows five example color pairs of confusion. As severity and type of color blindness can be very different, such color pairs are quite individual. I have chosen some colors in the color spectrum which I—as a strongly red-blind guy—can not distinguish.

As you can see, not only the base colors red and green cause problems. It is the mixture of the red part in the colors which makes colors indistinguishable for my eyes.

Remark: Moving in front of the computer screen or flipping the display fore- and backward can change the color perception a lot. Also if you print them out colors are perceived quite differently, specially from colorblind people.

On the other side not all reds and greens are indistinguishable colors for a red-green color blind person. Some greens and some reds can be seen and named even with a strong color vision deficiency.

Difference between red- and green-blindness

You know by now that red-green color blindness is actually just a generic term for any form of protan (red-blind) and deutan (green-blind) color vision deficiency. But what is the difference between those two or why are they often put together into the same pot?

Let us first have a look at the things those two different main types of color blindness have in common:

  • The main axis of colors of confusion is the same and so both types have the same main problem colors: red, orange, yellow, green, brown.
  • The genetic information is located at almost the same place on the X chromosome. Trichromatic vision developed much later in evolution while splitting the previous information of a single channel on red-yellow-green into those two different cone encodings.
  • The peak of sensitivity for red and green cone types is very close to each other. Trichromatic anomalies result in the shift of one of those peaks towards the other one.

On the other hand there are also some differences which makes it possible to split red- and green-blind people into two separate groups while testing for color blindness:

  • Red-blind people perceive the color red much darker. If you compare the results of Rayleigh matches—a color blindness test where you have to match yellow with a mixture of green and red—red-blind people use a much darker yellow to get a match.
  • The colors of confusion in the blue-purple area of the color spectrum are quite different. Red-blind people will mix in much more red and still can get a match between blue and purple.

But if you compare those two types with blue-yellow color blindness the differences in between them are very small. Therefore you will most often just talk either about red-green or blue-yellow color vision deficiency and forget about the rest.

By the way, if you think about the term itself and combine it with all the facts gathered together by now, you should know that red-green color blindness actually doesn’t really exist at all ;-).

In the next part of Color Blind Essentials you will learn more about the different possibilities to test your color vision and how good these tests really are.

Types of Color Blindness

In the first part of Color Blind Essentials we learned some fundamentals about color vision deficiency like the history, occurrences, causes, genetic inheritance patterns and more. With this second chapter I want to explain you the different types color blind people can suffer from.

But before we learn more about them we have to have a look at how color vision actually works. We have to do so because the functionality of the eye is closely related to the three main types of color blindness.

How color vision works

To see anything at all we need some tiny little helpers inside our eyeballs, the so called photorecptors. There are two different types of them: rods and cones. Both of them are sitting on the retina and pass information of light on to our brain. There are about 120 million rods which are very sensitive to light but not to color.

cone sensitivity

Cone Absorption Curves — © 2009 by Bruce MacEvoy

The cones are the photoreceptors which are responsible for our color vision. They are only about 6 to 7 million of them, gathering together very closely in the center of the retina, the so called fovea centralis.

And here comes the clue: Each of those cones is carrying one out of three different photopigments and therefore reacts differently on colored light sources. For each of this three types there exists a specific color absorption curve with peaks at different points in the color spectrum.

  • S-cones: sensitive to short wavelength light with a peak at ca. 420nm (blue)
  • M-cones: sensitive to medium wavelength light, peak at ca. 530nm (green)
  • L-cones: sensitive to long wavelength light, peak at ca. 560nm (red)

Mixing together the information of those three different types of cones makes up our color vision. This is also the reason that only three main colors are needed if we want to mix together all visible colors, because we only have three sources of information for mixing our whole color spectrum.

Types of color vision deficiency

Based on this knowledge about our visual system we easily can put together the list of different forms of color blindness. All of them have a direct relation to the available photoreceptors in your eye and are accordingly categorized.

  • Monochromatism: Either no cones available or just one type of them.
  • Dichromatism: Only two different cone types, the third one is missing completely.
  • Anomalous trichromatism: All three types but with shifted peaks of sensitivity for one of them. This results in a smaller color spectrum.

Dichromats and anomalous trichromats exist again in three different types according to the missing cone or in the latter case of its malfunctioning.

For a better understanding you can also call them blue-, green-, or red-weakness respectively -blindness. Unfortunately this terms didn’t really made their way and are not used very often.

You could ask know: “What about red-green color blindness or blue-yellow color vision deficiency? These are the ones I know but I can’t find them in your lists above.”

That’s right. The problem with this well known terms is, that they are not telling the truth! Many people think that if you suffer from blue-yellow color blindness this are the only colors you can’t distinguish. But that’s wrong. Color blindness doesn’t relate to just two color hues you can’t distinguish, it is the whole color spectrum which is affected. More on this a little later in this article and in the next chapter of Color Blind Essentials where we will have a closer look at red-green color blindness.

But to solve the puzzle: blue-yellow color blindness relates to tritan defects and red-green color blindness to all types of protan or deutan defects.

Type Denomination Prevalence
Men Women
Monochromacy Achromatopsia 0.00003%
Dichromacy Protanopia 1.01% 0.02%
Deuteranopia 1.27% 0.01%
Tritanopia 0.0001%
Protanomaly 1.08% 0.03%
Deuteranomaly 4.63% 0.36%
Tritanomaly 0.0002%

The above list shows you the prevalence rates of each type of color vision deficiency. The ratios between the most frequently occurring types for men can simply be remembered as: 1 protanope to 1 protanomalous trichromat to 1 deuteranope to 5 deteranomalous trichromats.

We already learned in the last chapter of Color Blind Essentials: What is color blindness?, that because of our genes more men than women are colorblind. Adding up all the numbers results in a total of 8% of men and 0.5% of women who are suffering from some type of color vision deficiency.

What do you see if you are colorblind?

We learned now a lot about the different types and categories of color vision deficiencies. But what does it really look like if you are colorblind? How do you see the world if you are colorblind? The four pictures below should give you a first impression.

Normal Color Vision Protanopia
Deuteranopia Tritanopia
The pictures above were generated with a tool called Coblis, which you can find right here on this web site.

If you have normal color vision you might realize that in the case of red-green color blindness (protanopia/deuteranopia) not only red and green colors are affected but the whole color spectrum is perceived differently. The same is of course true for blue-yellow color blindness (tritanopia). This is based on the fact, that all colors are perceived as a mixture of the three different cone types, and if one of them is missing the whole color spectrum changes.

The simulation below shows how the color spectrum changes. The shown lines are just meant as guides. Any line which ends in the so-called copunctal point connects the colors of confusion for a certain type of color vision deficiency. A more severe color blindness simply results in thicker and longer confusion bands.

Protan Lines

Deutan Lines

Tritan Lines


Simply put you can say, color blind people see the world like people with normal color vision see it at dusk or dawn. At this time of the day colors start to fade away which is comparable to a color vision deficiency.

To learn more about how color vision works and to get a lot of interesting details about this topic, visit the excellent web site of Bruce MacEvoy on Color Vision.

In the next part of Color Blind Essentials we will have a closer look at the most common type of color vision deficiency: Red-Green Color Blindness.

Booklet on Color Blind Vision

If you are looking for a nice little booklet about color blindness, which is easy to read and includes some very informative information on color vision, you have to have a look at Color-Blind: Seeying the world through different eyes.

The book consists of around 30 pages and it gets directly to the point:

“It is an invisible handicap, and those afflicted by it will certainly not shout it from the rooftops. That is probably the main reason why this anonymous group is hardly taken into account, except in a negative sense; ther still are quite a few jobs that are not accessible to the colorblind.”

Color-Blind: seeing the world
through different eyes

The author of the book is the founder of Blind Color, a company based in the Netherlands which tries to make the general public more aware of the existence of color blindness. They also help you to make your products to be color-proof for the colorblind and support companies, families and teaching institutes in all kind of topics related to color vision deficiency.

Starting with color in everday life, especially in a colorblind life, the book also covers the topic of how to do better when using colors for many different tasks. The last part is called color bilndness, its scientific explanation and focuses also strongly on color vision in general.

What I like very much in the booklet:

  • It includes many good examples about color blindness in real life.
  • A lot of color blindness simulating pictures strongly support the message.
  • There is a whole list of hints and tips for different industries what they have to think about when working with colors.
  • A very detailed description of color vision and the source of color blindness.
  • An explanation of the different types of color vision deficiency and their possible severities.

What I think could be done better:

  • Unfortunately the author doesn’t tell us a lot about possible career choices, which is often asked for by many people.
  • There is no information on different color blindness tests, color vision enhancements/tools, or about possibilites to cure color vision.
  • Some of the simulated pictures don’t seem to be correct. The color red is sometimes rendered much to dark (I’m strongly red-blind and still can spot a huge difference between the original and the simulation).

Overall it is a compact booklet about color blindness with some really good tips. You can easily learn the basic facts of color vision and its deficiencies, but if you want to learn some more details in certain topics which I mentioned above, you need further sources of information.

The booklet either in English or Dutch can be ordered directly from the Netherlands at

My friend from was so nice to send me an issue of this booklet. Thanks. And if you speak Dutch you should also visit his very comprehensive site on color blindness.

What is Color Blindness?

About 8% of all men and 0.5% of all women are colorblind. The most common form is red-green color blindness which affects much more men than women, as it is encoded on the x-chromosome (sex-linked) and usually inherited from a mother to her son.

But Color blindness is not ‘color blindness’! There are still many people who think colorblind people can’t really see any colors. But the term is misleading. More than 99% of all colorblind people can see colors. A better wording would be color vision deficiency, which describes this visual disorder much more precisely.

So what actually is color vision deficiency also known as color blindness?

Simply put, if you are suffering from a color vision deficiency you are perceiving a narrower color spectrum compared to somebody with normal color vision.

This short definition raises a few more questions which need to be answered to understand the term color-blind more completely:

  • Why am I suffering from color blindness at all?
  • What means narrower color spectrum compared to normal color vision?
  • Are there different types of color vision deficiency?
  • How do I know if I’m colorblind?
  • Is there some possibility to cure color vision deficiency?
  • Can I just live with it or do I have to be afraid of it?

In this article I will among other things answer the first two of those questions. The others will be looked at in the follow up articles of this series about Color Blind Essentials. But first of all I would like to take you back to the 18th century.

History of color vision deficiency

The first scientific paper about color blindness was written by John Dalton in 1793 entitled Extraordinary facts relating to the vision of colours. Dalton himself was red-green colorblind and as a scientist he took interest in this topic. He claimed, that a colored liquid inside the eyeball is the source for a different color perception. This was proved wrong only after his death, when his eyes were examined and no such liquid was found.

After that Thomas Young and Hermann von Helmholtz were the first who described the trichromatic color vision. And once a theory for human color vision was ready, the basics of color vision deficiency weren’t far away.

The cause of color blindness

Color perception in the human eye is build up by three different types of cones. Each type is sensitive to a certain wavelength of light (red, green, and blue) and every perceived color is therefore a mixture of stimuli of those three cone types.

Now, if you one of those peaks of sensitivity is shifted towards another one or if one is missing at all, you perceive a narrower color spectrum—in other words you are colorblind. As a peak can be shifted everything between a little bit and the whole way, any type of severity is possible. The closer the peaks are the more severe is your color vision deficiency: slightly, moderately, strongly, or absolutely colorblind.

“What do you mean by «narrower color spectrum»?”

Let’s say somebody with normal color vision can identify and distinguish 150 hues. If you are colorblind this number starts to drop as you have fewer possibilities to create color mixtures from your color receptors. In case of absolute color blindness—missing one type of cone at all—you might be able to distinguish only as many as 20 different hues!

The type of affected cones also has a big impact on your color vision deficiency. As there are three different types of color receptors, there are also three different main forms: red (protan), green (deutan), and blue (tritan) disorders. As red and green deficiencies result in quite comparable color vision problems, they are put together and known under the term red-green color blindness. You will find more information on the different types of color blindness in the following two articles of this Color Blind Essentials series.

Much less common possibilities for color blindness are also glaucoma, aging, alcohol missuse, or a hard injury on your head. Those factors often cause some milder form of blue-yellow color blindness (tritanomaly). Also other facts like signal transmission can cause problems in color perception, but this is not fully understood yet.

Why am I suffering from color blindness?

You know now the cause of color vision disorders, but we still have not evaluated why we can be colorblind at all.

We learned that in most cases color blindness is a genetic disease which is inherited from the parents to their children. This means, if one or both of your parents is suffering from some type of color vision deficiency, there is a certain chance that you or your children will have the same vision handicap. The chance is strongly related to the type of color blindness.

Before I show you a sample inheritance pattern, we will have a closer look at our chromosomes. Unfortunately it is not as simple as it could be, because there are different chromosomes involved in color vision. And on top of that even on the same chromosome several different genetic code pieces are participating. The essence you should know is, that red-green color blindness is a sex linked recessive trait and blue-yellow color blindness is a autosomal dominant trait.

  • sex linked: encoded on the sex chromosome X; men only have one of them (XY) compared to women (XX).
  • autosomal: encoded not on the sex chromosome, equal for men and women.
  • dominant: if it is encoded on one chromosome, you really suffer from it.
  • recessive: if you have another healthy chromosome, it won’t show up.

If you combine this all together, we have more colorblind men than women. — Why is that?

Color blindness inheritance pattern

Red-Green Color Blindness Inheritance Pattern

Red-Green Color Blindness Inheritance Pattern

The above genetic encodings lead us directly to the inheritance pattern. This will also show us on a glance, why there are more men suffering from color blindness than women.

The diagram on the right shows the inheritance pattern of red-green color blindness, which is by far the most common type of color vision deficiency. As you can see, this is a disorder which is passed on from a grandfather to his grandson, whereas the mother is only a carrier of it. A carrier is not affected because the trait is recessive. This causes much more men to be red-green colorblind, and even more women to be carriers of this color vision deficiency. You can also learn from this diagram, that a woman can only be red-green colorblind if both of her parents are at least carrying the disease encoded in their genes.

Am I the only colorblind person?

No, definitely not. Color blindness is a very common disease which is found all over the world. Different scientific studies show, that roughly 8% of all men and 0.5% of all women are colorblind. This numbers are supported by different studies and are about the same all around the world. The high difference between men and women is resulting from the facts we just learned, that the most common form red-green color blindness is a recessive sex-linked trait.

Knowing this numbers you can also compute some very interesting probabilities in color vision deficiency:

  • Approximately every 500st handshake is between two colorblind people.
  • It is almost sure (probability: 94%) that at least one out of a football team is colorblind.
  • If you pick 100 persons randomly, there is a tiny chance (< 1.5%) that none of them is colorblind.

In the next article of the series Color Blind Essentials, we will have a closer look at the different types of color blindness. The common and also the very uncommon ones.

Color Blind Essentials

Many people are looking for the basics about color blindness. So I wrote the following series on Color Blind Essentials which should give you a good overview over the most central topics.

You will not only learn what color blindness really is, which forms of it exist and of course some details about the most well known red-green color blindness. But you will also have the possibility to read more about on how a color vision deficiency can affect your everyday life, if there is a way to cure or at least soften it and the different possibilities to test your color vision.

If you would like to read the whole series offline, just click at Free eBook: Color Blind Essentials and get a handy PDF including all the articles of this series.

This series on Color Blind Essentials includes the following six parts:

If you want to learn even more about color blindness and closely related topics, you can either follow some of the links I provide in this series, directly dive into the articles archive of Colblindor, search the whole web site or subscribe to my latest articles.

New Color Blindness Tests Sets Minimal Requirements for Professional Flight Crew

The current situation can be quite frustrating. If you want to become a pilot you have to follow a complicated color vision test regulation. And even then most weak colorblind applicants are still rejected which seems to be an unfair decision.

Color Assessment & Diagnosis Test

Because of the lack of reliable, standardised tests and the absence of information on the specific colour vision needs of professional flight crew, the UK Civil Aviation Authority supported by the US Federal Aviation Administration initiated this study.

A team around Prof Barbur from the Applied Vision Research Center in London was mandated to find the minimum color vision requirements for modern flight crew, and a new color assessment and diagnosis test. This was the last part of the study after The Use of Colour Signals and the Assessment of Colour Vision Requirements in Aviation and a Task Analysis which included two operating case studies: the Airbus A321 and Boeing 757.

Dr Sally Evans, Chief Medical Officer at the CAA, says:

“The current diversity in colour vision testing methods and standards demonstrates the need to adopt more objective assessment techniques internationally. If the assessment methods and limits derived from this study were applied as minimum requirements for professional flight crew, 35 per cent of colour deficient applicants would be eligible for medical certification as a professional pilot. The CAA intends to promote this research internationally with a view to gaining acceptance of the CAD test and its incorporation in world-wide medical standards for pilots.”

This sounds very promising for all colorblind pilot applicants! So let us have a closer look at what this new color blindness test is all about and how they reached this new results.

Color Assessment & Diagnosis Test

The current procedures within JAA for pilot applicants are unsatisfactory for at least two reasons.

  1. There is no guarantee that the deutan subjects that pass secondary tests can cope with safety-critical, color-related tasks, since the severity of their color vision loss remains unquantified.
  2. Many color deficient subjects that can carry out such tasks safely fail the lantern tests and will not therefore be allowed to fly.

This findings and many detailed studies on color vision deficiency resulted in a new color blindness test, the color assessment & diagnosis test (CAD test). The subject’s task is to report the direction of motion of a colored square on a gray square background with dynamic luminance contrast noise. This new developed color vision test has shown in a broad study to be very accurate in identifying type and severity of one’s color blindness.

The subject’s color vision severity is measured in Standard Normal units (SN units). If your result would show a red-green threshold of 2 SN units this would mean, that you need a twice as strong color signal compared to a average standard CAD observer. This threshold can be quit different for deuteranomalous and protanomalous observers as a limit to pass the PAPI test. Details on this are shown in the conclusions.


The Precision Approach Path Indicator (PAPI) was indicated as the most important, safety-critical task that relies largely on color vision. On this basis a PAPI simulator test was developed to quantify the severity of a pilots color vision deficiency which is still safe to fly. This simulator can be used in controlled laboratory environments.

PAPI Test Simulator

The simulator reproduces both the photometric and the angular subtense of the real lights under demanding viewing conditions when the lights are viewed against a dark background. Since other color-related tasks such as seeing the color of the parking lights or the discrimination of runway, center-line, red and white lights are less demanding, it is assumed that the pilot will also be able to perform correctly these tasks.

The aim was to identify type and severity of color vision deficiency which cause problems with the PAPI test and correlate those results to the CAD test results. In principle, this approach should make it possible to recommend pass/fail limits based on the observer’s ability to carry out the most safety-critical and demanding PAPI task.

Principal conclusions

Safe to Fly:
36% Deutans
30% Protans
35% Overall

The very promising results suggest that subjects with minimum color blindness that does not exceed 6 SN units for deuteranomalous observers and 12 SN units for protanomalous observers perform the PAPI test as well as normal trichromats. If these findings were adopted as pass/fail limits for pilots ~35% of color deficient applicants would be classed as safe to fly.

  • When the ambient level of light adaptation is adequate, normal aging does not affect significantly either red-green or yellow-blue thresholds below 60 yrs of age.
  • Analysis of PAPI results shows that the use of a modified white light results in significant, overall improvements in PAPI performance.The modified white is achieved simply by adding a color correction filter.
  • 43 of the 77 deuteranomalous subjects failed the PAPI test. 29 out of the remaining 34 subjects that passed the PAPI test had CAD thresholds < 6 SN units.
  • 20 of the 40 protanomalous subjects failed the PAPI test. 13 out of the remaining 20 subjects that passed the PAPI test had CAD thresholds < 12 SN units.

The study also concluded that the administration of the CAD test eliminates the need to use any other primary or secondary tests. When one includes normal trichromats, ~94% of all applicants will pass the so called fast-CAD screening test and be classified as safe to fly. This process is very efficient since the fast-CAD test is simple to carry out and takes less than 30 seconds to complete.

Official CAA news:
CAA research paves the way for more people with CVD to become pilots
CAA Paper 2009/04:
Minimum Colour Vision Requirements for Professional Flight Crew