Red-Green Color Blindness Doesn’t Exist

Hey, everybody knows that red-green color blindness is the most common type of color vision deficiency. How can I claim that it doesn’t exist at all? – I’ve got not only one but three reasons which support my statement that there is no type of color vision deficiency which really deserves the name red-green color blindness.

Red and Green Peppers

Only Gray Peppers?

When you realize or get told that one of your friends is colorblind, most probably you remember the term red-green color blind and try to imagine, what this means:

  • My friend can neither see red nor green?
  • He can’t distinguish those two colors at all?
  • Besides red and green he has no problems with colors?
  • Or maybe red and green look like gray to him?

This is all wrong and the reason why I say, that there is no such form of color deficiency which should be called red-green color blindness. And here are my three arguments which strongly support the sentence: Red-green color blindness doesn’t exist.

(1) Red-green color blindness doesn’t exist, because there are really two distinct forms: red-blindness (protanopia/protanomaly) and green-blindness (deuteranopia/deuteranomaly). Protan defects are caused by a shift of the peak of the red sensitive cones in your eye towards the green peak, or if they are missing at all. For deutan defects the same is true for the green sensitive cones. And even if the naming sounds like a combination of both, you are suffering just under one of them.

(2) Red-green color blindness doesn’t exist, because if you are colorblind you will encounter problems with colors from the whole color spectrum. There is no such color vision deficiency which is only focusing on certain colors like red or green. The so called confusion lines can give you a quite good understanding of how a color spectrum is seen by color blind people.

(3) Red-green color blindness doesn’t exist, because if you are really colorblind, you really can see only in gray. This is called monochromacy or achromatopsia, which affects only a handful of all color blind people. In this case it doesn’t make sense to talk about any colors at all. On the other side, if you have only problems with your red, green or blue sensitive cones, this isn’t actually color blindness but some form of color vision deficiency. Or as I put it in another article: Color Blindness is not ‘Color Blindness’.

If you still think, that you are suffering from red-green color blindness, have a look at Which Type of Red-Green Color Blindness is It? and learn more about the real type of your color vision deficiency.

Foto taken by Martin LaBar

Colblindor Featured in Vision Testing: A Blind Spot In Occupational Safety

Occupational Health & Safety is the industry-leading news magazine, eNewsletter, and website for occupational health and safety professionals. The February issue 2009 will feature the topic “Vision Testing: A Blind Spot In Occupational Safety”, including web links to Colblindor, as a resource about color blindness.

What is the article all about?

The author claims, that vision is often not checked regularly if you compare it to hearing or blood pressure. And this causes that many employees are short sighted, have no depth perception, are night blind, or are suffering from color vision deficiency—unrecognized from their employers—whereas this handicaps can be real safety problems.

As an employer you should ask yourself:

  • When did your employees have the last vision check?
  • Is some aspect of vision crucial for their job?
  • Should you introduce some vision tests in the recruitment process?

I can’t judge all aspects of the article. But I can judge the part about color vision, which is unfortunately not very well researched. All they say is that color blindness could be a problem for drivers because of the traffic lights. I think this is a bit to superficial. You can find my opinion on this topic at: Colorblind at the Traffic Light.

Anyway, thanks for linking me up.

Colorblind Colors of Confusion

When people hear that you are red-green colorblind, most of them think, that you can not distinguish between red and green. But that is wrong.

Of course, red and green are some of the problem colors when you are suffering from red-green color blindness. But…

  • … some shades of red and green are easily to distinguish,
  • … and many other colors also cause problems.

The following diagrams of the CIE 1931 color space can give you a quite good understanding of which colors are problematic for colorblind people.

Protan Lines

Deutan Lines

Tritan Lines



All colors in the direction of the lines might be hard to differentiate. There are three different diagrams corresponding to the three main color vision deficiencies: protanopia (red-blindness), deuteranopia (green-blindness), and tritanopia (blue-blindness).

Copunctal Point x y
Protan 0.747 0.253
Deutan 1.080 -0.800
Tritan 0.171 0.000

See Wyszecki & Stiles, Color Science (2nd ed.), 1982, Table 1 (5.14.2) p. 464

The lines shown above are called confusion lines and converge at a point which is called the copunctal point. For the three different types of color vision deficiency there are three different copunctal points.

For the two types of red-green color blindness (protanopia and deuteranopia) the main problem area of colors is really in the axis between red and green. And on this side of the color space, the confusion lines are quite the same for both types. This is why they are called red-green color vision deficiency. But on the left side of the diagram you can see that they are quite different confusion lines which show the problem colors.

If you would like to learn more about color matching and confusion lines you might like to read the article Color Matching and Color Discrimination by Joel Pokorny, a very well known researcher in the field of color vision deficiency.

As you can see from the above diagrams, the whole spectrum of colors is some way reduced for colorblind people. It is definitely not only red and green (protanopia/deuteranopia) or blue and yellow (tritanopia) which can not be distinguished.

Online Anomaloscope doesn’t Differentiate Red-Green Color Blindness

RGB Anomaloscope

The RGB Anomaloscope can be used to check if you are suffering from red-green color blindness or not. Unfortunately it is not possible to differentiate between the different forms of red-green color vision deficiency.

Our online anomaloscope is based on matches between yellow and a mixture of red and green—like the real anomaloscope. The matches you make can tell you, if you are suffering from red-green color blindness or not (because if you are not colorblind, you can’t make any matches).

In an earlier update of the anomaloscope (Severity Upgrade), I found an interesting looking pattern in the matching colors. We had two peaks which looked like a pattern for differentiating between red- and green-blindness.

  • Red-blindness shifts the peak of red sensitive cones towards the peak of the green ones. Because of that you have problems in differentiating certain colors and also your red starts looking much darker.
  • Green-blindness works the other way around. The peak of the green sensitive cones is shifted towards the red peak. This causes a very similar form of color blindness, but in contrast to red-blindness, red doesn’t start to look darker.

Over the last month I tried to evaluate this pattern in further detail while asking testers to declare their type of color vision deficiency, if known. Unfortunately I couldn’t find any pattern at all.

RGB Anomaloscope Greenblind

RGB Anomaloscope Greenblind

This diagram shows the number of people taking the test, which declared to be green-blind and matched a certain yellow value (horizontal axis) to either green (#00FE00) or red (#FF8000).

The above diagram can’t tell us anything about a pattern. We have to compare it to the diagram, which is based on the numbers from people who declared to be red-blind.

RGB Anomaloscope Redblind

RGB Anomaloscope Redblind

I adjusted the vertical axis in this diagram, as there were more people who declared to be red-blind. So the two diagrams can be compared 1 : 1.

Unfortunately the two diagrams Greenblind and Redblind look pretty much the same. This shows me, that my first assumption was wrong and this version of the RGB anomaloscope can not differentiate between red and green color vision deficiency.

50 Facts about Color Blindness

#01 99% of all colorblind people are not really color blind but color deficient; the term color blindness is misleading.

#02 Red-green color blindness is a combination of red-blindness (protan defects) and green-blindness (deutan defects).

#03 Color blindness is more prevalent among males than females, because the most common form of color vision deficiency is encoded on the X sex chromosome.

#04 “What color is this?” is the most annoying question you can ask your colorblind friend.

#05 There are three main types of color vision deficiency: protan, deutan, and tritan defects.

#06 Strongly colorblind people might only be able to tell about 20 hues apart from each other, with normal color vision this number raises to more than 100 different hues.

#07 Colored lenses or glasses can improve color discrimination in your problem areas but can not give you back normal color vision.

#08 Ishihara plates are the best known color blindness tests, but they are not the most accurate ones.

#09 About 8% of all men are suffering from color blindness.

#10 Severity of color blindness is usually divided into the following four categories: slightly, moderate, strong, and absolute.

#11 The terms protan, deutan, and tritan are Greek and translate to first, second, and third.

#12 A father can’t pass his red-green color blindness on to his sons.

#13 Dogs are not colorblind.

#14 Color vision deficiency would be a much better term; but it is not as easy to pronounce compared to color blindness.

#15 There are people which are really suffering from complete color blindness, which is called achromatopsia or monochromacy.

#16 Blue-yellow color blindness would be better called blue-green color blindness, as this are more the problem colors.

#17 There exists every nuance of color vision deficiency severity, starting from almost normal color vision up to complete color blindness.

#18 Protanopia, deuteranopia, and tritanopia are types of dichromacy, which means you have only two different color receptors (cones) compared to three with normal color vision.

#19 If a woman is red-green colorblind, all her sons will also be colorblind.

#20 Colorblind people feel handicapped in everyday life, and almost nobody recognizes this.

#21 99% of all colorblind people are suffering from red-green color blindness.

#22 When using color correcting lenses you are wearing two differently colored lenses in your eyes.

#23 Red-green color blindness is a recessive sex linked trait, which causes more men to be colorblind than women.

#24 John Dalton wrote the first known scientific paper regarding color blindness.

#25 Protanomaly, deuteranomaly, and tritanomaly are types of anomalous trichromacy, which means you have three different color receptors (cones) like people with normal color vision but one of them is shifted in its peak.

#26 In certain countries you need normal color vision to get a drivers license.

#27 Deuteranomaly—one form of red-green color blindness—is by far the most common form of color blindness.

#28 More women than men are carriers of color blindness, even though they are not colorblind themselves.

#29 Some people get rejected from a job assignment because of their color vision deficiency.

#30 About 0.5% of all women are suffering from color blindness.

#31 Blue-yellow color blindness is a dominant not sex linked trait, which means both men and women are equally affected.

#32 Red-green color blindness doesn’t mean that you are only mixing up red and green colors, but the whole color spectrum can cause you problems.

#33 The anomaloscope is the most accurate color blindness test known today.

#34 Police officer, firefighter, and airline pilot are the most famous jobs which require normal color vision.

#35 There is no treatment or cure for color blindness.

#36 Pseudoisochromatic plates were introduced by Professor J. Stilling of Strassburg in 1883; the Ishihara plates by Dr. Shinobu Ishihara followed almost half a century later.

#37 Different chromosomes are involved as sources for the different types of color vision deficiency.

#38 Women can also suffer from color vision deficiency.

#39 Monochromacy—also called achromatopsia—means you have only one type of color receptors (cones) in your eyes.

#40 Color blindness is also called Daltonism, after the scientist John Dalton.

#41 The most often used types of color blindness tests are: pseudoisochromatic plates, arrangement test, and the anomaloscope.

#42 Better color vision deficiency terms would be: red-blindness for protanopia, red-weakness for protanomaly, green-blindness for deuteranopia, green-weakness for deuteranomaly, blue-blindness for tritanopia, and blue-weakness for tritanomaly.

#43 John Dalton believed his whole life that the cause of his color blindness is a colored fluid inside his eye balls.

#44 Many colorblind people have problems with matching clothes and buying ripe bananas.

#45 Quite a lot of people with normal color vision can’t pass an Ishihara plates test free of errors.

#46 The International Colour Vision Society is scientifically investigating every aspect of color vision and color vision deficiency.

#47 Confusion lines of the CIE 1931 color space show exactly the colors of confusion for all forms of color blindness.

#48 Only a whole battery of color blindness tests can reveal the true type and severity of your color vision deficiency.

#49 John Dalton was also colorblind himself.

#50 A Colblindor is a colorblind person who learned to enjoy his colorblind life ;-)

Photoshop CS4 Accessibility Enhancement Incorporating Color Blindness

Photoshop CS4

Photoshop CS4

If you are designing graphics for a web page you have to keep in mind to make them also accessible to colorblind persons.

With Photoshop CS4 Adobe introduces soft proofing for color blindness, a great support just for this task.

The new soft proofing filters for color vision deficiency were developed in corporation with the Japanese Color Universal Design, a user-oriented design system, which has been developed in consideration of people with various types of color vision, to allow information to be accurately conveyed to as many individuals as possible.

Adobe Photoshop CS4 supports the following two color blindness filters, which combine the two most common forms of color vision deficiency:

Photoshop CS4 Color Blindness Option

Soft Proofing on Color Blindness

To determine whether your document is CUD-compliant or not, step through the following three simple steps:

  1. Convert the document to RGB color mode, which provides the most accurate soft proofs for color blindness.
  2. To simultaneously view the original document and a soft proof, choose Window > Arrange > New Window (optional).
  3. Choose View > Proof Setup > Color Blindness, and then choose either Protanopia-type or Deuteranopia-type.

To comply with CUD, you have to check your document in both views.

If you are a graphic/web designer, don’t forget to check your graphics on accessibility for colorblind users. Photoshop CS4 is one of the tool which can help you to fulfill this task—the color blindness simulator Coblis another (online) one. You might find some other helpful tools on my list of 15 Tools If You Are (Not) Colorblind.

Thanks to Jay Kinghorn and his article on Photoshop CS4: Color Blindness Proofing. You can also find more information on color blindness validation at the Adobe Photoshop CS4 accessibility overview.

Color Blindness: Can Colored Contacts Help You?

Many people who either newly learn about their color blindness or who would like to get a job which requires normal color vision, are looking for a way out. As there is no cure for color vision deficiency, improving color vision with lenses for the colorblind seems to be a nice possibility.

The question arises now, can such colored contacts really help you if you are colorblind?

Colored Glasses

Possible view through colored glasses.
Photo taken by Malingering

The following discussion refers to a product called ChromaGen, most probably the best known colored contacts aiming to help colorblind people.

The ChramaGen: A practitioner report is the most often cited report about visual aids for colorblind people. Unfortunately this source seems to be very optimistic and more like some surreptitious advertising.

It is well known, that colored contacts can only alter the perceived colors but can not enhance the spectrum. For example Dr. Natalie P. Hartenbaum states very clearly that lenses don’t correct color blindness contrary to some of the vendors, which make it look like as they could cure color blindness with their products.

ChromaGen lenses

Colored contact one eye only

Unfortunately I can not tell you anything about my personal impressions as I have never tried such lenses. But I would like to cite some others who did try colored contacts in hope to find something against their color vision deficiency under certain circumstances or even in everyday life.

Faborito says the following about his ChromaGen lenses (Link):

My life has changed in a way a have no words to describe. Last year i saw red for the first time in my life. Is amazing!!!! You have no idea what is like to see a coke can or a tomato in full brilliant red. It’s spectacular. I used them every day, and for photography are great.

Tabascokid is also sharing his story about the Chromagen lenses (Link):

[…] The thing that is not explained in the brochures is that despite you suddenly having a broader range of visible colours, depth perception and contrast, it doesn’t help in actually recognising the colours. When I attempted to edit skin tones and subtle casts, I was still just as much in the dark. The primary colour looked lovely and punchy but I never really had issues with these anyway. Tones and hues were as confusing as ever. My brain still couldn’t get the differences.

Chris made the following experiences (Link):

With ChromaGen only one tinted lens is worn, this provides colour contrast but I found it distracting as I was unable to coordinate the contrasting visual data. Although I passed the Ishihara Colour Test with this system, I was still unable to name colours. The ColorView system changed the colour spectrum but at the expense of darkening the visual spectrum overall. This system was more akin to wearing sunglasses than anything else as I still was unable to identify colours confidently and still failed the colour test.

Azmole tried the two systems ChromaGen and ColorView (Link)

I did have some improvement when testing them with the Ishihara test. The opthamologist with Colorview had me go outside in daylight to use the lenses and many reds that I normally could not see came into view. I did not purchase the lenses because I was more interested in passing a color vision test and felt even with the lenses I would fail.

Now judge yourself if you wont to give colored visual aids a try to improve your color vision. But you have to know, that not one product can cure color blindness but only alter your color perception.

Read more details about colored contacts and glasses at Improving Color Vision with Lenses for the Colorblind.