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

Genetic Screenings for Color Blindness

The Clinical Testing Laboratories at New Mexico State University will cooperate with the Genevolve Vision Diagnostics Inc. to start genetic screenings for color vision deficiency and to work towards a possible gene therapy to cure color blindness.

Jay Neitz from the Neitz Color Vision Lab could just recently cure some colorblind monkeys and also developed a genetic color vision test. Building upon this basis in this new partnership they want to develop a new standard for color blindness tests and possibly have a breakthrough in curing color deficient patients.

Matt Lemelin, the founder and CEO of Genevolve:

“Our goal is to establish a new world standard for color vision testing and to increase public safety while providing a diagnosis that doctors may discuss with their patients. With this process, we can now diagnose the type of colorblindness and the extent of deficiency with amazing accuracy and precision.”

Lemelin also lists some of the reasons, why such a genetic color blindness test is a need today:

  • Age: Todays color blindness tests often require a minimal age of at least 5 years. This could potentially affect a child’s development.
  • Memorizing: Persons can memorize a test and alter the result. This could be very dangerous for some specific jobs.

I personally believe that a genetic test is only needed because people themselves want to have something fool-prove. A test which tells them the truth about their color vision, which is not influenced by some doctors judgment. Of course a fool-prove test also makes the testers feel more safe. But I don’t really think that the above two statements are true:

  • Children don’t have to be tested much earlier. They can’t grasp the concept of color yet and don’t need special assistance in daily life until they recognize it themselves.
  • Arrangement tests, anomaloscopes and lanterns can’t really be memorized. And even a plates test only needs a shuffle to unmask any potential cheater.

Anyway, the colorblind community is definitely looking forward to get an accurate color vision test which can be used as a standard for many job specific vision tests and as a matter of course a gene therapy to cure color blindness. We will wait patiently for further news…

You can read the whole article from the NMSU here: DNA lab at NMSU partners with company to fight colorblindness. And don’t miss the latest breakthrough in color blindness gene therapy of monkeys.

Can the Sun Change Color Perception More Than a Mild Color Vision Deficiency?

Brett wants to become a pilot. But he is suffering from a mild form of color vision deficiency which disqualified him.

He is now looking for any possibility which could show, that in some cases weak colorblind people are not less suitable than people with normal color vision as there are many factors which can have quite an impact on your performance and which you always have to be aware of.

Read his request, you might be able to help him:

I have been diagnosed with mild deuteranomaly and have been disqualified from USAF pilot training. I am currently working to get an exception to policy that would allow me to still go to pilot training, and I know how difficult this will be. But I need help with research for my exception to policy package. Today I came up with a simple but interesting idea and tried researching but was unable to find the information I need.

The idea is that since I have mild deuteranomaly, my M (green) cones are shifted a few nanometers towards the L (red) cones. I also know that many other factors can affect the color perception of people with normal color vision, such as the position of the sun in the sky, weather, hazy, cloudy, etc… So what I’m looking for is a measure of how much the position of the sun would affect the color of an object. I’d bet the bank on the sun shifting light wavelength more than my condition.

I’ve looked into color temperature a bit and found at dusk or dawn sunlight has a color temp of approx. 3200 K and at noon its around 6500 K. My problem is I’ve been unable to relate this change of 3200 K to 6500 K to a change in wavelength (nanometers).

Any information on how much the sun would affect color perception, or how many nanometers a person with mild deuteranomaly would be shifted would be greatly appreciated.

I can be contacted at:

After reading his thoughts you maybe realized that your situation is quite similar. Hereafter you can read his whole story which might help us all to find a better solution to the problem, that many colorblind people are rejected from a job just because of some color vision tests, which are most of the time to unspecific and much to restrictive.

So I’ll start my story about 3 years ago when I began applying to become an Air Force Pilot through OTS. I was in my senior year at Virginia Tech working on my degree in Aerospace Engineering. After turning in my application to OTS I had to wait a while for the boards to make their decision, so I asked to have my flight physical done so that I would know if I was medically qualified before I even entered the Air Force. With the exception of distant visual acuity everything went well and I was given a waiver for my vision (20/200 uncorrected). I passed the PIP1 color vision test with 13/14 each eye. Unfortunately I ended up not being accepted to OTS and was quite disappointed.

Searching for what’s next, I found the possibility of a 2-year AFROTC program I could do while working on my Masters degree. I looked at school and was accepted to Embry-Riddle Aeronautical University’s Aerospace Engineering Master’s program and the AFROTC program their. During my first year their I was selected for a Pilot slot before even going to field training.

I went on to complete my work at Embry-Riddle and commission 3-MAY-09. I had to sit around all summer waiting to EAD but finally did on 3-SEP-09 and began to long drive to Laughlin AFB to wait for ASBC at the end of October, IFS, and someday UPT. I’ve been at Laughlin for just over a month now and received orders to go to Brooks AFB last Wednesday for MFS (Medical Flight Screening). At MFS they did a a few tests, but the only thing I was a bit worried about was my distant vision waiver. All of my tests went fine except for color vision. I scored 10/14 for the PIP1 for each eye failed a few other tests. They kept me for additional color vision tests and determined that I have hereditary red-green (deuteranomalous) green-weak, color deficiency. This is completely disqualifying for Pilot, Navigator, ABM (not sure about this one), Combat Control, Combat Rescue, Special Tactics Officer, OSI, Test Pilot School as an Engineer, and 99% of Astronaut positions.

This has been quite devastating since all of those jobs I listed have been my dreams and backup plans in case my dreams didn’t work out. Having them all stripped away in one day has motivated me to fight this to the end. I’ve been researching quite a bit to come up with anything I can do. I don’t really know who to contact but I’m planning to start with my commander. I plan to tell my whole story and explain why I believe I am fit for at least one of those jobs.

I’ve gone my entire life (24 years) without knowing I had any form of color deficiency and have accomplished a lot; I just don’t see how it can be so bad that I would be at a disadvantage now. I’ve read about potential advantages that red-green colorblind people have such as better night vision (which I found one paper going against this), being able to see “faster” (I haven’t found any scientific evidence), and most notably being able to see through and detect camouflaged objects more easily (still don’t have a solid source, just mentioned in other sources).

From what I can tell the only way I might be able to get around this is to get my commander or someone above him to write an “exception to policy” that would basically say that they are willing to take a risk on me since I might be able to make up for a deficiency with other aptitudes. Other than that, political figures may be able to use their pull somewhat to get me around this (but I know none personally).

If anyone has any information that may be useful to my cause please contact me at Otherwise I’ll be busy looking for other careers (which don’t require perfect color vision) that will be as exciting, dangerous, noble, and challenging (both mentally and physically) as that of an Air Force Pilot.

Color Update on D-15 Color Blindness Test

The D-15 Color Arrangement Test is running online on Colblindor for quite a while now. But unfortunately the colors weren’t perfectly accurate.

old and new example colors

Yves contacted and told me about this error. What happened? I forgot to perform the chromatic adaptation from D50 to D65 for the sRGB color space. This means I actually assume the XYZ values were taken under a white-blueish D65 light while in reality they were measured under D50 which is white-yellowish. This means I have overestimated the red and underestimated the blue.

Today I updated the test with the new values. The used colors should now be correct and ready to try out: Online D-15 Color Arrangement Test.

I you’ve taken the test previously the result won’t change that much as the colors are just slightly shifted in the color space. My results were still very unpromising: Strongly color blind!

Richard’s Life as a Color-Blind

Richard was so friendly to write his answers in detail on The Color Blindness Project Questionnaire. Thanks! I thought putting this together into an article by itself makes it more public to other interested readers. So the here are his answers:

When did you first discover you were colourblind?
My parents suspected when I was about 4. I could arrange the vivid primary coloured blocks of my toys, but anything less than vivid, crayons, clothes food, I was misidentifying what colour they were.

A trip to The Natural History Museum in London with an exhibit on the eye, and on colour vision, confirmed this when I did all the classic misreading of the Ishihara test. By the time the formal colour test rolled around at school, it was pretty much a foregone conclusion.

How did you discover you were colourblind?
Well aside from being told the story above, it was for me, being simply unable to colour things in correctly or recognise colours.

  • For years, my anti-smoking posters at school had cigarette butts in brightest green.
  • My Union Jack was easy to identify: It was purple and orange.
  • All my drawings throughout my youth were in my own special palette.

And it continues. There was a lot of hoo-ha in the news recently about our beloved British brand Cadbury being taken over by US Multinational Kraft, “the famous purple wrapper” the newsman announced. — Purple? I’m 29. I had no idea. I thought it was blue.

What are the issues/problems you have faced being colourblind?
Well disability, let’s just define that, depends on how society is organised. What I have is an altered sensitivity to the spectrum, this only matters when things are categorised by colour, then I am adrift in a canoe without a paddle.

An example, only a trivial one, I was attending a job interview and the waiting area was a calendar which denoted all the religious festivals of about 10 different faiths. The key was colour code and the days and months were festooned with little coloured dots, which were meant to be wonderfully informative about which religious festivals fell on which days. I couldn’t tell them apart. Moreover if someone had been there and said what about that one, what colour is that? I’d have been guessing. I’ve gotten pretty good at that: guessing. And false positives are self correcting.

I see what I think are the colours but I have very little ability to tell them apart. I’m a diagnosed protanope so very strong red blind, and this cuts a swathe through my sensitivity to reds, greens, browns, yellow, oranges, and the pseudoisochromatic colours with which I can (and do) confuse them.

Thus, red can appear black or dark grey, but not always. Blood for instance to me looks brown, very dark. I do see a red – coca cola cans for example, but I’d bet what I think of as red probably isn’t and is very much dependent on the context. Take my coca-cola red and put it on a snooker table and I bet I’d confuse that red with something else. That’s why grass is green. Of course grass is green. But green in other contexts is where hue, and brightness combine to confound me.

  • Blue and purple, covered that one.
  • Orange and certain browns.
  • Yellow and green.
  • Grey, certain greens and pink are completely interchangeable.

Everyone all thinks traffic lights are hard, they aren’t – not really. You learn them by sequence. What they aren’t is the right colours. The two red and amber, to me look like slightly different species of yellow. And the green at the bottom, is white – it looks like an ordinary light bulb.

Of slightly more difficulty are brake-lights. Recognising those from tail lights is hard. I’ve hit the brakes hard, once to often now to believe that I’m not just a bad driver.

How did you overcome the shortcomings?
I have very sympathetic parents. My brother is the same, so they coped with both of us down the years.

Teachers, I think don’t get it. And I don’t blame them. Colours are a second alphabet. People assume you know what they are talking about. Even when you tell them, if they remember at all, it’s rare that they alter their behaviour.

And what do you tell them?

I’m colour blind?

What you can’t see colours? …yes..but..I..can’t tell them apart.

What colours’ this [ ]* then?

*[ ] insert nearest object here.

and that’s how it usually goes.

Colour vision deficiency takes longer to say, as does the explanation, and I prefer it but I don’t think it helps people understand. I’d prefer they had a solid grounding in colour-theory instead.

It’s taken some time for me to get my head round it, but I am not sensitive (cannot see) certain hues. The hues I can see are modulated by brightness. A sufficiently bright green is as yellow to me. Purple’s an interesting one, because what is reflected is blue and red light, I can detect the blue, I am insensitive to the red, all purples are species of lighter or darker blues.

My solutions are if it’s important that it’s coloured I label it. It is simply no good relying on me to see a colour and recognise it. I need that second level of information like a name written down. Second, I ask people. I’m pretty up front about saying I’m colour blind – I can’t see that. What colour is it? That usually works, with the above caveat that no-one has any idea what I’m actually talking about.

In my own life it was pointed out to me, that I shop for clothes by texture, I’ll go around scrunch up shirt sleeves and jumpers to see how they feel, what they look like is secondary. My wardrobe also reflects a certain bias. Lots of blues (which I can see) Lots of dark colours, greys, a few greens (definitely green not pink) and black.

What else can be included/excluded in the guide book for parents other than the ones described above to make it more comprehensive?
Oooh. I wouldn’t want to frighten them. An introduction to Ishihara—as that is what they will likely encounter and have to sit with their child through, what it means and how it diagnoses.

I think I would personally want an easy to understand overview of what colour is (wavelengths of light), the idea of a colour gamut, a colour space, (RGB etc). And then how colourblindness changes that. How the Ishihara dots are painted in the pseudoisochromatic colours that exist in those spaces for people like me who lack sensitivity to one of the spectral colours of light.

What it means: not that my world is uncoloured. I swear to you it isn’t. I just have no idea what those colours are called. It’s rather like having a virtuoso chef who can create all the world’s dishes out of only three ingredients. A little of this, a little of that, a pinch of the other and *foompf* Egg salad nicoise. And then taking away one his ingredients. Yes he can still make all those different foods in all the variety, but without that extra thing, everything he makes is just the little bit more bland and samey. You can’t really tell them apart anymore. That would be flavour blindness. I’m colourblind in the same way.

Thank you very much Richard for this great insights.

PS: Richard updated his answers and polished them even more. You can find his latest answers on the color blindness survey at Further Adventures in the Land of the Colourblind