Color Blindness Myths and Misunderstandings

October 25, 2010

Topics: Accessibility.

I’ve always believed that web site accessibility depends on an understanding of accessibility issues — not on technical issues. Obviously, knowing the technical side of web site construction and how it impacts accessibility is very important. Some decisions are fundamentally technical, but a huge part of web site accessibility is purely visible — and just understanding accessibility issues will make a huge difference.

To that end, here are a few quick comments about color blindness. Color blindness (or color perception deficiency) is an issue for approximately 1 in 12 people, mostly men. However, color perception problems are not always very effectively diagnosed, so these numbers could be low.

Color blindness is an inability to see certain colors.

Color blindness is really a misnomer. People with various types of color blindness are better described as being color vision deficient: it’s an inability to distinguish colors, not an inability to see color. People at the furthest limits of color deficiency, however, may have such an extreme inability to discern colors that this can be a fairly accurate description.

Individuals with color vision deficiencies can’t see red.

Well, no. Assuming we’re discussing Protanopic or Deuteranopic color blindness, in which the individual is missing either the red or green sensitive cones, the actual problem is that they may not be able to distinguish the color red. The color isn’t readily differentiated from other hues of the same shade or tint. Red perception deficiency is certainly the most common type of color vision deficiency, but it’s certainly not true of all individuals with poor color vision.

You have normal color vision

Not really. In fact, color perception is a spectrum for all of us. What’s commonly referred to as color blindness is actually only the portion of that spectrum which is considered anomalous — where the ability to perceive color begins to impinge on normal interactions with the world. Having “normal” color vision simply means that you don’t generally experience problems because of your color vision. You may well still fail an Ishihara test.

Color perception deficiencies are inconvenient, but don’t pose any serious problems

Particularly in our modern, technological society, color perception is a critical part of comprehending the world around you. From LED indicators which blink red, green, or yellow; to weather maps which a spectrum from red to green indicating storm severity; to knowing what color a traffic signal is showing if you’re in a location with a different signal orientation than what you’re familiar with. Outside of technology, color deficiencies can impact recognizing that you’re developing a severe sunburn or knowing whether you’ve actually cooked that hamburger enough to be safe.

People with Color Perception Deficiency have better Night Vision

Actually, I couldn’t definitely verify this one way or the other. There are a number of claims that this is true, but the reasoning is highly variable and not particularly evidence-based. It’s possible that certain types of color perception deficiency may give people better night vision, but it’s also possible that since some types of color perception deficiencies cause people to be photosensitive, those people may feel like their night vision is better, simply because it’s much better than what they’re accustomed to. Regardless, any evidence which is reasonably definitive would be appreciated.

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37 Comments to “Color Blindness Myths and Misunderstandings”

  1. I’m red/green colour blind. My observation is that with aircraft during the day I cannot identify or recognise the colours of the wingtip navigation lights, but at night I have no difficulty at all. They are crystal clear.

  2. I only see white too black so greys in between..
    Why has no1 else mentioned it

  3. That was an interesting question to research. The actual code doesn’t seem to stipulate exactly what constitutes “passing” color vision tests. It simply states that

    The color sense must be determined to be satisfactory when tested by any of the following methods or an alternative test acceptable to the Coast Guard, without the use of color-sensing lenses:

    Then provides a list of tests, but doesn’t define what “satisfactory” means. There was no further detail describing what the reasons are for applying restrictions, but I imagine those would be wrapped up in what “passing” the test means. Since there’s no indication of exactly what constitutes passing or failing the color vision test, it could be something that’s left up to the discretion of the test administrator – but I don’t know!

  4. I am partially red-green color deficient. The USCG therefore restricts me to daylight operations only. Can you find out why this restriction exists, given that some articles imply that night vision may actually be improved. I have no problem identifying solid red, green, blue and yellow whivh apparently allows me the daylight operations license/medical approval.



  5. Keeping in mind that my colour vision issues are mostly red green related, I do have a really weird set of issues at night.

    For some unknown reason, my vision at night tends to bathe everything in the colour green.

    For example, even on clear nights, I have found that the sky has a very slight green tint too it. This green tint is much stronger while I’m looking at the moon, which actually appears to have a lime green aura around it whenever I look at it.

    Clouds, fog, and rain all make this effect much more pronounced. At night, clouds and fog appear as being lime green, with a brightness that is comparable to that of daylight. Rain also has a very similar effect at night.

    Snow is similar, but produces a much less pronounced colour change. Snow storms at night make the sky appear a green grey colour, with again, a similar brightness to day light.

    In the absolute dead on night (so you know, no light sources at all), I often find I can see better then others, though its harder to describe that feeling.

  6. There is evidence, albeit limited, that color blindness improves low-light vision.

    “Scotopic vision in colour-blinds”(1998) by S. Verhulst and F.W. Maes.

    Their findings show that individuals with color blindness have improved low-light vision and that this (along with improved camouflage penetration abilities) might be a key reason why color blindness was not selected out of our ancestors.

  7. I am red/green colorblind. There are lots of obvious disadvantages, but I have found a couple advantages: 1. While fishing, I can see the fish deep in the water while those with normal vision cannot see them. This helps a lot when stream fishing. 2. At night, I can certainly see much better than those with normal vision. This comes in handy during mountain hikes and camping with very little light. I could make a list of several hundred disadvantages…..Ron

  8. I can mirror the experiences of others here, regarding sight in darkness. I am red/green colorblind and I used to do nightwalks with friends and I spotted obstacles on the road or stuff in the tree sidelines way before them. When it got really dark they sent me forwards as a ‘scout’

  9. As a child, I could see all the numbers in the color blindness tests. By the time I graduated high school, I could only see 75% of them, and by my fifties I could only see half.

  10. I have a documented case of red/green cvd. My wife can see colors of many varied shades, and even knows the names of most of them. She, however, readily admits she can’t see in the dark at all. I’ve noticed that it needs to be really REALLY completely dark, like literally cut off from any light source at all, for my eyes to not soon adjust to where I can start to see what’s around me. It’s not scientific but it’s my experience. I also noticed that I can clearly see what cameras can’t.

  11. I have red-green deficiency.

    And I wonder if anyone else ever experienced what I call “The Christmas Headache”? You open up the Sunday paper, the adverts spill out, and the top one has a green background and red letters, or vice versa) in keeping with the Season. You look at it for a few seconds and it starts to throb. After a little while you start to get a dull headache. It goes away as soon as you avert your eyes. Am I the only one?

  12. Google “reverse color blind test” and you’ll find some evidence that we do have better night vision 😉

  13. This is my issue: red, blue, purple, some shades
    of bright green on the computer are black. Orange is
    brighter than yellow. Browns are grey and most
    greens like street signs and informational
    signs are white lettering on a white back ground
    Yellow is always yellow. Does this make sense to

  14. Back in the nineties, some friends and I went camping in the desert east of San Diego, California. One night, one of us had the dumb idea to go on a short night hike with no flashlights and only a sliver of moonlight to go by. I knew I was red-green colorblind, but hadn’t heard anything about superior night vision. I was the only one among us to go home without legs full of cactus needles, and was alone in being able to see a faint “moonbow” in a light mist that rolled through.

    I’ve since done informal tests with “chromies” (friends with normal eyes), and they definitely can’t see as much as I do at night.

  15. I am not sure exactly what type of colourblindness I have, if anyone could provide a link to a test that accurately tells me what type I have it would be very appreciated. It seems I get different results on every single test. This has always frusterated me because the tests always tell me that i’m red/green colourblind, yet not once in my life have I mixed up those colors! I have always been completely unable to tell blue and purple apart though. (Also all 6 of my male cousins have some sort of colourblindness, though most of them have red/green) And I will 100% attest to the fact that some people with colour vision deficiency have better night vision. The first time I really noticed it was when I was playing goalie in street hockey at a young age and the bright yellow tennis ball got shot past the net and into someones yard. None of my friends could see where it was (as it was pitch black outside, it was probably close to 11pm, we were just about to quit for the night) but I could CLEARLY see where the tennis ball was located. I couldn’t just see the outline or anything, I could look at the yard and see the tennis ball, no searching or guessing required. My friends were amazed, and I’m now notorious in my peers for having extremely good night vision.

  16. Better night vision proof? Go on a trek with me through the Okinawan jungle at night. I’ll take point. And… try to keep up or you will get lost.

  17. @Strange It’s certainly accurate to call me one of little faith – that was, in fact, the entire point of this exercise! Prior to this post, I had read a few articles indicating that the color blind had better night vision; but had no evidence. Not being inclined to trust on faith, I was curious to see if anybody else had evidence.

    I still haven’t found evidence, per se, but I do have a much larger volume of stories, which certainly leads towards the probability that it’s true.

    Thanks for contributing your story!