City University Online Color Vision Test

The City University of London has a well know Department of Optometry and Visual Science. They invest a lot in research for color vision and color vision deficiency which includes their own color vision clinic.

A well known color blindness test called City University Color Vision Test is available in a print version and often used to identify tritan deficiencies. This test is derived from the well known D15 color arrangement test and is based on different plates, where out of four dots the one which comes closest to a fifth dot has to be selected. If you only have very mild form of color blindness, you will pass this test. But on the other side the City University Test allows to identify the type and approximate severity of color blindness.

City University Test

Can You Spot It?

Now for all of us, looking for a way to test one’s color vision abilities online, they developed a web based color vision test. The test is a little (very uninteresting) movie, consisting of pictures which look like the one right here. In each picture there is a square, which might be hidden if you are suffering from some type of color blindness.

The movie is twelve Mb long, so you need a fast link to play it. But if you can play it, you will have to chance to find out if you are suffering from some type of color blindness. There are some facts which are really great about this test:

  • The test is not only made to detect red-green color blindness, but also for people suffering from blue-yellow color blindness. This is not often the case. Specially the well known Ishihara Plates tests are only for red- or green-weak respectively -blind persons.
  • Different severities of color blindness are covered within this test. If the square is not visible to you for only a few seconds, there is a big chance that you are suffering some type of color vision deficiency.
  • It’s the most simplest color blindness test, covering a big range of deficiencies. You only have to watch and see, if you always can spot the square.

There is of course also a downside to this. Through this movie you won’t find out how severe it is and which type it is. You don’t even get a feeling, because you don’t know if you can’t see the square for let’s say ten seconds, what this means. Is it just a mild form of color blindness or not? Only the eye specialist will be able to tell you for sure.

Maybe you already have downloaded the web-based color vision test and watched the movie. If the square disappeared for you for some time, you might like to compare your results to my ones. From other online tests and what my doctor told me once upon a time I know, that I have some form of very severe red-weakness or red-blindness. And my test results are:

  • Square disappeared 1. time from 0:16 through to 0:26.
  • Square disappeared 2. time form 1:04 through to 1:11.

What are your results? It would be great to have some others to compare with. But always keep in mind, that online color blindness tests can’t tell you the truth because there are to many factors like display settings and illumination which affect the test results. To get a proper screening you have to visit your eye specialist.

Color Blindness – Reason for a Job Rejection

One reader of Colblindor was so kind to write me his story about a job rejection because of his color blindness. It’s not a severe color vision deficiency he is suffering from and the job is mostly down with computer support, but he was still rejected.

Well, yes I was declined for one job for my red-green blindness. It was a job in the area of car paint development (research and development). I have worked in the past in areas that have something to do with color (formulation an equalizations) and it never represented for me a problem (I have to say that some times I noted that some colors were harder to make equal than others, but nothing more…). The doctor said that I wasn’t able to do my job.

By now I am trying to demonstrate that I’m perfectly able to that that job. Principally because the equalizations process doesn’t base upon the only eye of the human, the coloration process is carried on with the support of scientific instrumentation, like colorimeters and spectrometers, a lot of times more objectives and exacts than the weak human eye…

Note: Do you know what is the worse about been rejected for a job? They don’t even tell you why, they just say you…”a problem with the vision” :(

Were you ever rejected for a job because of your color blindness? It would be great to hear more about it.

Contribution by Israel F.F. Thanks a lot.

Mixing Up Blue and Green

Are you mixing up blue and green? What about red and green? It’s not only the color green which causes problems to colorblind people, but how can you know which type of color blindness causes the confusion, specially when it affects your child?

My son will be four this year…. It appears that he sees and can recognize all colors except for certain blues and greens. Sometimes he can point out a deep blue, however he often mixes up lighter shades of each. Is this Tritanopia? Or some version of it?

Before we get into some more details about colors and types of color blindness, I would like to state my thoughts on age and recognition of color blindness.

Already a few month old toddler has the same color spectrum as an adult. But only at the age of two they can start naming colors. And again it takes quite some time until a child really can grasp the whole color spectrum. Therefore a four year old child might need still some more time to learn all the colors. I think first of all you should wait two more years to finally judge about color blindness. There is still enough time at the age of six to consult an eye specialist and check for color vision deficiency.

On the other side it’s a good age to learn about color blindness and try to understand, how the world looks different to somebody with color blindness. You can learn how to support your child with everyday tasks and you might get a better understanding, why certain things are not that easy to accomplish as a colorblind child (or adult).

Mixing up blue and green
Every colorblind person can have problems distinguishing blue and green, no matter which type of color blindness. Why is that?

If you suffer from any type of color vision deficiency, you have quite a different color perception compared to somebody with normal color vision. They can distinguish more than 100 different hues. Color blindness reduces this, down to just around 20 different color hues with a severe color vision deficiency.

The CIE color space shows the whole color spectrum. When looking at the confusion lines of the CIE color space, you will recognize, that blue-yellow colorblind people definitely have problems with the color axis going from blue to green. But on the other side, if you are suffering from red-green color blindness, your spectrum of different distinguishable hues can be very limited. Because green flows into blue it can also cause problems between those two colors.

Therefor it’s not easy to tell which type of color blindness you are suffering from, when you can’t tell apart some shades of green and blue.

You have to learn more about the color vision deficiency affecting your child. Maybe some tests could help you to improve your knowledge. It’s definitely not easy to do those test with a four year old. In this case the color blindness testing poster could be of some help. But as I explained above, there is still enough time to learn more about it and otherwise there is always the possibility to visit your eye specialist, which is also the only way to receive a correct diagnosis.

Do You Have to Order Your Markers to Know Their Colors?

How can you remember the color of your markers or crayons if you are colorblind? You can not, if you don’t use any trick which helps you to remember the colors they have.

The following reader question reached me a few days ago and points out this well known problem. Everybody suffering from color blindness will remember the time, when he had to use some kind of a system, when the marker box was to large to tell the different colors apart from each other.

My friend claims he is red-green and blue-yellow colorblind and said that as a kid had to put all of his markers back in the box in order so that he would know which color was which in school. I know the receptors in the eye are red, blue, green, and yellow? So can he see any color at all?

I would like to split this question into three different parts, each one covering a one part of the above statements.

He is red-green and blue-yellow colorblind. To chance to suffer from both types of color blindness at the same time is very very very low. If you really suffer from blue-yellow and red-green color blindness, you will definitely mix up a lot of colors. But on the other side, even if you are red-green colorblind this doesn’t mean you only have problems distinguishing red and green but many different colors like: orange/green, blue-green/gray/purple, red/dark-green/brown, and more.

The receptors in the eye are red, blue, green, and yellow. Well, that’s not quite right. With normal color vision you’ll have three different color receptors which are most sensitive to blue, red, and green respectively. If you are colorblind, at least one type of color receptors is either missing at all (dichromatism) or the peak of sensitivity is displaced (anomalous trichromatism).

So can he see any color at all? Yes, he can see colors and does not only precept shades of gray. There is only one exception to this, when you are suffering from achromatopsia (monochromatism). But as he can use markers he must be able to see some colors. When you are colorblind you still can enjoy a very colorful world, which is just less colorful compared to somebody with normal color vision.

So each one who is colorblind needs a trick to handle the problem of an oversized marker box. I also remember the time at school where I just knew by heart which crayon had which color. When I had to use the box of a friend of mine, I was lost. And unfortunately this doesn’t stop with marker boxes but accompanies you through your whole life.

You have to learn colors and remember them, again and again, and of course you get better when growing older. Don’t you?

Are Colorblind People Disabled?

If you are colorblind, do you feel disabled? And what does the law say about it? Do others have to take some precautions, in a way that colorblind people are not excluded because of their handicap?

There is an interesting discussion going on at boagworld.com, if color blindness has to be looked at as a disability or not. In this case looking at the UK law and their Disability Discrimination Act (DDA). The question is not easy to answer, because there are many different types of color blindness and the law doesn’t really name any disability, but just describes them.

You might like to join the discussion at Are colorblind people disabled?

Do you think color blindness is a disability or not?

16 Essential Questions about Color Blindness

Courtney is doing a Graduation Project on the topic Color Blindness and was asking me for some help. She put together a list of 16 questions about color vision deficiency which I would like to answer hereafter.

Actually not all of the 16 questions are on the topic of color blindness. We are starting with some simple questions about myself. But after that we are heading right into some fundamental topics. And with each question going deeper into more details, after reading through all of them, you will have quite a good overall picture about color blindness.

  1. What is your name?
    Daniel Flueck. (Actually it’s written with two points above the u and without the e afterwards: Flück. But this is my international standardized name :-)
  2. What is your field of work?
    I’m working in the IT education, which means my day to day job has nothing to do with my engagement for this weblog about color blindness. It’s only the interest into the topic and my own color blindness which drives me to put together some hopefully useful informations.
  3. Do you have to be licensed or certified to perform your work? What is the license called?
    For my job; not really. But as I wrote above, my job has nothing to do with color blindness. And for my weblog writing I also don’t own a licence yet ;-)
  4. What is your educational background?
    I have a masters degree in mathematics. Again something completely different. Sorry for that. But starting with the next questions I can hopefully give you some more satisfying and accurate answers.
  5. What is color blindness?
    Color blindness is a biological condition, where you can’t distinguish the same broad spectrum of colors as somebody with normal color vision. The term stands for anything between almost normal color vision and the most pronounced form, where you can only differentiate shades of gray.
  6. Who is mainly color blind, males or females?
    Mainly males suffer from color vision deficiency. This is because the most common form of color blindness is provoked by some variations on the X chromosome—also called sex chromosome. Because women have two such chromosomes, they have the chance to overmodulate the defective one. On the other side, men have only one X combined with a Y chromosome and therefore suffer more often form color blindness.
  7. How do you know you are color blind?
    My family found out about my color blindness when I was in kindergarten and painted a sky in a nice pink. They also were aware of color blindness because my father also suffers a mild form of it. Only when I was twenty years old I did a simple check up at the ophthalmologist to get it confirmed.
  8. How does an optician or an ophthalmologist test for color blindness?
    Actually I really don’t know. But I fear that most of the time they only have some Ishihara plates to test colorblind persons. For proper testing you also would need some other tests like an University test for blue-yellow color blindness and of course an anomaloscope to get an accurate test on red-green color blindness.
  9. At what age should people be tested for their ability to see colors?
    Parents should be aware of color blindness specially with boys, because almost 10% of all men have some type of color vision deficiency. If you think that there could be a problem you might test it in kindergarten, because if you know about it, you and the teachers can give better support to your child. On the other side if you are not sure how good your color vision is, you can test it before you decide on your later profession, because there could arise some major problems.
  10. Is there a reason that color blindness is important to diagnose? Why?
    First of all, I don’t think it should be tested in general. Only if you have some concerns a test can help you very much to classify them. It is important to diagnose color blindness, because only then you can take proper precautions to help for example your child with homework.
  11. What tests do you go through to find out if you are colorblind or not?
    There are many different tests for color blindness. Some of them are based on images, others need a special equipment and today you even have some computer based tests. It’s always good to use different tests for an exact diagnosis. The most famous color blindness tests are the Ishihara plates, many colorful dots showing a number in an other color which is not visible for a colorblind person, or the anomaloscope, where you have to adjust a mixture of red and green to the brightness of yellow.
  12. Are there treatments to cure color blindness?
    No, there are no treatments for any color vision deficiency. There are some lenses, which try to enhance the color vision but otherwise you just have to get around with it. Maybe in the future there will be some possibilities in genetic manipulations, but there is still a very long way to go.
  13. Is there a cure for color blindness?
    For most people suffering from color blindness there is no cure. But there are some forms of acquired color blindness: A hard hit on the back of your head can cause blue-yellow color blindness. With this type of acquired color vision deficiency there is a chance that normal vision will come back after some time. But again, there is no treatment to enforce it. You just have to wait and hope for the best.
  14. Are you aware of any specific jobs that color-blind people could not perform?
    The most talked about job which can not be taken by a colorblind person is pilot. Because pilots have a big responsibility and almost everything in a cockpit and outside works with some color coded signals, it wouldn’t be a good choice of job if you have some kind of color vision deficiency. There are also problems to apply for police officer, and you might have some disadvantages in biology/chemistry and as an electrician, because of color coded wires.
  15. How does color-blindness interfere with the performance of those jobs?
    Some jobs like pilot just can’t be done and that’s ok. In other jobs a colorblind person will have some handicaps which have to be overcome with creative solutions. You might need some extra help on colors from your workmates to accomplish certain tasks. But every colorblind person will find out himself, if a job can be done as desired and if the chosen job is the right one concerning their deficiency.
  16. Is color-blindness a genetically inheritable trait?
    By far the most cases of color blindness are inherited from a mother to her children, and not as often thought from a father to his son. But there are some possiblities of acquired color vision deficiencies. Aging, heavy alcool consum, toxic ingredients, some eye diseases and even a hard hit on your back head can also cause color blindness to a certain degree. If you are suffering from such an acquierd form, you wan’t pass it on to your children. Therefore color blindness is not in all cases a genetically inheritable trait.

If you like to get some more information on certain topics you can follow some of the links below.

I tried to put together some short and accurate answers. Browsing through Colblindor, you will find some more detailed answers on many topics discussed above. If you like to get updated on the latest issues about color blindness, you can subscribe to my RSS feed.

Stop Asking! – Top 5 Questions You Should Never Ask Your Colorblind Buddy

As there are up to 10% of all men colorblind, you definitely will bump into one sooner or later. Or you just found out, that your old buddy is colorblind and you didn’t know it for that long.

To prevent you from putting your foot in it, I will offer you the top five questions you should never ask your colorblind colleague, partner, friend or neighbor. Why shouldn’t you ask those questions? Simply put: They just make you look like a fool and also make your buddy look like a fool.

Those five questions are not irrelevant. You should know the answer to those questions but don’t get them while asking somebody. Therefore I will not only list those five questions and leave them up to you but also will show you, why you shouldn’t ask each question and in the same breath answer them for you.

Color Blindness: Top 5 Questions Not to Ask

#1: What color is this?
Don’t ask this question, just don’t do it. This is something you make a colorblind person feel like a fool and you can’t take any profit out of it. Somebody suffering from color blindness doesn’t see other colors, they see less colors or maybe some colors closer to each other, because they see fewer differences in hue.

And if you would think about it before asking this question you will find out yourself: No answer given to this question will help you to understand how a colorblind persons sees the world. And that is actually what you want to know.

#2: Do you see only shades of gray?
There are very few people suffering from monochromacy. Those people only see in shades of gray. But they also have problems with bright light and need to wear often sunglasses.

This kind of color blindness is very very rare and there is only a tiny little chance, that your buddy will suffer it. So every other person suffering form color blindness sees colors, but less colors. With normal color vision you can distinguish more than 100 different hues. A colorblind person might only be able to distinguish 20 of them, but still can see colors.

#3: Which colors do you see then?
All colors, many colors, less colors. Nobody suffering from color blindness can answer you this questions correctly. Some may see more, some less but none can tell you which colors, because a colorblind person doesn’t know how you see the world.

If you nearly close your eyes your vision is comparable to colorblind vision. Also in the break of dawn the visible colors can be compared to what somebody suffering a color vision deficiency sees.

#4: Who buys your clothes?
Me; who else? Yes; going shopping for a new shirt and tie isn’t the easiest thing for a colorblind guy. And it’s sometimes embarrassing, not to know if the chosen colors fit together and fit into your wardrobe. This is something that accompanies you for your whole life if you are colorblind.

There are different strategies to handle this. Either you ask somebody else, every time until you just know the pieces which fit together. Or you adjust the colors you wear to colors you know that they will always fit together.

#5: Hey; you shouldn’t drive a car!
I know, this isn’t really a question. But it transfers to the question in your mind: How can a colorblind person distinguish between the red and the green at the traffic light?

Usually this is not a problem at all. The chosen colors for traffic lights are enhanced to make them more visible to colorblind people. Some extra orange and blue are mixed in, so everybody should see the difference. An other clue which helps a lot is the arrangement: Red at top/left, green at bottom/right. All this together minimizes the problem for somebody suffering from color blindness almost to nothing.

So don’t put your foot in and make yourself a fool. Try to ask some interesting questions which can get you into a nice and interesting talk about color blindness. I’ll have a look at such intelligent questions in a future post. Stay tuned.

How Can I Tell if My Friend is Colorblind?

The reader question below points out a very delicate topic. Not everybody wants to admit to others and even more importantly to himself, that he or she is colorblind. And because color blindness is not something which is obvious and you know anyway like your height, it’s not easy to find out if such a person really is colorblind or not.

How can I tell if my friend is color blind? Are there certain colors he will wear or certain things he will do? I think he might not want to admit it, but I wonder. I am afraid to ask. I don’t want to hurt his feelings.

As written in the question, somebody confronted with a maybe colorblind person, which doesn’t like to talk about it, is in a uncomfortable position. Should you start talking about it and ask? Or should you just sit back and wait until you’ll find out anyway?

I will offer you two different ways to tackle this impasse. As I recommend the offensive way warmly to you, the defensive way can be an equally valuable path for you to follow along.

But before we dig into some possible solutions, we have to have a closer look at the term colorblind. As there are many different types of color vision deficiencies, it’s important to know what we think of when saying my friend is colorblind.

By far the most common form of color vision deficiency is red-green color blindness. About 8% of all men are suffering some type of it. Actually red-green color blindness can be split into four different subtypes. But all of those have a lot in common:

  • Red-green colorblind people can see many colors but differentiate them more in terms of brightness and saturation than hue.
  • The color axis red-orange-yellow-green-brown is the most challenging if you are suffering it.
  • There is also a line of colors ranging from blue-green to gray and over to some purple hues which are difficult to tell apart.
  • If you are suffering only a mild form of red-green color blindness you might even not be aware of it.
  • A lot more men than women (< 0.5%) are affected.

There are some other types of color blindness, however they are only very rarely observable. Knowing this basics lets us reformulate the question to the more precise statement:

How can I tell if my friend is red-green colorblind?

The Offensive Way: Ask him.
I know, this doesn’t sound like the right way to you. But it’s definitely the best way. Let me tell you why and how you can do it.

First of all you have to learn about color blindness as a not colorblind person. You will find a lot of material about it on Colblindor or on the web. Some interesting facts are:

  • Color blindness can occur in very mild forms which are no handicap in everyday life.
  • Colorblind people often have problems to match the right clothes, know when a fruit is ripe or if they have a sunburn.
  • If you are colorblind, you often can’t spot red/orange/yellow blossoms and flowers.
  • There is no cure for color blindness but most people easily learn to get along with it without feeling handicapped.

If you learn more about the challenges of a colorblind person, you can offer appropriate help. You not only have to wait every time until you get asked (or often not get asked) but just help out as it would be the most normal thing. This can be a great support for a colorblind person, for example in a shop when he likes to buy a new cool tie which of course should match his shirt.

Through your knowledge about color blindness you can go the offensive way and ask him. But not only ask if he’s colorblind, he might not even know it. Tell him, how you could support him much better in some everyday tasks and how it could help you a lot more to understand how he sees the world.

You might like to ask him to have together a look at some color blindness tests and find out if he has some deficiency and how severe it is.

Color blindness is nothing to be ashamed of, there are to many of us.

The Defensive Way: Don’t ask him.
Often you really feel to afraid to ask or you don’t want to hurt his feelings. Therefore I would like to explain you some ways which might help you to find out if your friend is colorblind or not.

Shopping for Fruits. A colorblind person often has problems distinguishing a ripe fruit from a unripe or even an overripe one. If he often buys unripe bananas this might be a clue.

Matching Clothes. If you are colorblind you can not match your clothes very well. You can’t see which colors do match and therefore often either wear only few colors like black and white or otherwise wear sometimes clothes which do not match in color at all.

Pastel Colors. I can’t tell you why, but colorblind people tend to prefer pastel colors. Not always, but more often then people with normal color vision.

Colored Crayons. A huge box of colored crayons, this is some of the worst which can happen to somebody suffering from color blindness. Usually a colorblind person chooses a small box of color crayons with not to many distinct colors which are always in the same order and well distinguishable.

Colorful Flowers. When wandering around or in your own garden, if you are colorblind you definitely will have some problems spotting nice flowers and blossoms. Usually from the distance you wont see them; everything might look green to you. Only coming closer or if your friend tells you about them, you will be able to see for example red or orange flowers.

Cooking Meat. If your friend is colorblind, he also will have some problems to tell if meat is cooked well just from the color. The color change is usually to small to spot and he often will ask somebody else for a judgment.

Skin Color. Colorblind persons have problems to see slight changes in skin color. They don’t see if somebody goes pale/green and looks sick or if he has a sunburn or not.

Maybe through this seven hints you will be able to find out if your friend is colorblind or not. If you have the strong feeling, that he really has some type of color vision deficiency I would like to encourage you also to think about the offensive way and finally ask him.

I hope this tips were of some help to you to find out about the color blindness of your friend or just to learn more about your colorblind partner. Maybe you also would like to know How to Support Your Colorblind Husband which includes some more advises how to handle color blindness if it doesn’t affect you yourself but your partner, friend, workmate, …

Carnival of Colors III – Open Eyes

For the third issue of Carnival of Colors we leave the hitherto topic trace of color names to sally out some new fields.

As there are so many colors around us every day and every minute—if you don’t close your eyes—I would like to encourage you to walk around with Open Eyes this time.

The following six submissions to Carnival of Colors III are based on a broad range of topics. But all of them can teach you how to open your eyes to colors in a certain way. Enjoy.

Open Eyes

« Verlee gives us an introduction into Choosing color combinations and shares the best clue for the source of your color inspiration: Always keep your eyes open for color combinations that you like. Follow it and read more of her inspirations at Verlee’s blog »

« Michael digs even deeper into color combinations for a Room Color and How it Affects your Mood. He concludes that this is a good starting point in your search for a paint color. So open your eyes and feel your colored moods and maybe some more tips from freshome will help you to find the right color for you. »

« Maybe you don’t like to refresh your rooms with a new paint but just with some great color photographs. You can learn from Christopher How to use color in your photographs. Again you should open your eyes for the color in your life to take some great shots on your personal Photographer’s Journey »

« When Sassy from The Mommy Journals was trying out some macro photography shots, she definitely had to open her eyes to find this small imprint on her bottle of green tea about the Ingredient: natural color. What?? An industry gag about artificially added natural color, just to catch the latest wave of a more nature friendly mindset? »

« Mike says: One needn’t be restricted to the culinary arena to enjoy the pairing of wine and bird. I recommend that you start looking outside your kitchen for such delights. Not only one from his 10,000 birds can say Color Me Vinaceous—which means either wine-colored or containing wine. Reading through the article lets me think, it’s both: Bird watchers containing wine naming birds wine-colored. »

« If you had to much of red-wine the Germans would say you are blue. So this is the last call to open your eyes. Watch out for blue neighbors, blue toys or other blue heroes. Alejna is Collecting Tokens and did put together a list of blue-skinned, blue-furred or in any way blue creatures. It’s just so blue. »

Stay tuned for the next release of Carnival of Colors which will be released the first of next month. If you would like to contribute just contact me or visit the Carnival of Colors Blog Carnival Page.

Orange Spring Blossoms

At the moment the weather feels more like summer than anything else. But it’s still springtime which also means that all the blossoms shine in many different beautiful colors.

Orange Spring Blossoms

Orange Spring Blossoms


A few days ago I posted a picture about some red spring blossoms which beautify our garden. You want believe it, but just besides this bush where I didn’t recognize the shiny red blossoms, is another bush in the middle of its bloom carrying orange blossoms. And of course, you already will have guessed it, I didn’t see them till my wife told me about it.

The orange blossoms are even harder to see than the red ones. For my eyes orange looks almost the same as green. So it takes quite an effort to spot the difference. Due to my red-blindness (protanopia) an orange whatever will definitely never stand out in a green surrounding.