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.
John T Folsom; December 5, 2021 at 3:50 pm
Combining research into the literature, education in the fields of physics and astronomy, training in orienteering and naval operations, and personal experience, I think I can posit an explanation for why some colorblind individuals report having better night-vision.
As part of orienteering and naval operations I was taught to only use red lights at night because blue light can be seen from further away in darkness. This mirrors what I learned at university: the longer wave-lengths of red light are less energetic and therefore require higher concentrations of light to reach a detectable threshold.
Given that the vast majority of colorblind individuals are red/green deficient, it is unsurprising that some portion of these people have developed a greater sensitivity to blue light. This may be due to either biological processes within the eye or improved processing within the brain: research would be required to determine the correct mechanism(s).
Persons who are more sensitive to blue light (or more accustomed to operating without red and green light) would have an obvious advantage operating in conditions where low light levels have approached the minimum threshold for detection within the eye.
Frank Simpson; January 18, 2020 at 10:56 pm
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.
Suzannah Richards; October 29, 2018 at 1:40 pm
I only see white too black so greys in between..
Why has no1 else mentioned it
Joe Dolson; April 21, 2018 at 11:03 am
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
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!
Paul Flagg; April 21, 2018 at 9:43 am
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.
Connor; February 7, 2018 at 5:48 pm
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.
AJ; August 31, 2017 at 8:48 pm
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.
Ron Davis; July 17, 2017 at 10:22 pm
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
Statistx; October 23, 2016 at 7:49 am
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’
Bill Anthony; August 2, 2016 at 7:08 am
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.
David DM Coutant; November 17, 2015 at 12:05 am
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.
Bezukhov; May 7, 2015 at 1:51 am
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?
Xardas; March 25, 2015 at 5:27 pm
Google “reverse color blind test” and you’ll find some evidence that we do have better night vision 😉
darla reinhardt; January 24, 2013 at 9:32 pm
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
Jim; June 7, 2012 at 9:26 pm
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.
Caden; December 1, 2011 at 9:22 pm
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.
Point Man; March 13, 2011 at 10:29 am
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.
Joe Dolson; March 8, 2011 at 4:11 pm
@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!
Strange&SillySavage; March 4, 2011 at 4:36 am
O Yea of Little Faith! I was drafted because of my peculiar phase shifted “color-blindness” ability to see very subtle shades, naturally enforced from birth “mental training” to differentiate objects by outline and texture, and superior night vision which is more than double a “normal” persons contrast in low level light. All of my abilities were well verified by extensive vision and field testing by our military. So I got to be point man on every night patrol, the guy with the crossbow who took out sentries, forward spotter/observer ashore to call in fire from ships and aircraft, and a helicopter gunner (which I really hated!). Yes, In our last forever war in Southeast Asia, I saw and killed the “camo” clad enemy before they saw me! So for me, my “color-blindness” is a curse and a blessing. A curse because it sent me to war, and a blessing because it helped me survive it!
T. Chandler; January 21, 2011 at 9:09 pm
I’m moderately to severely colorblind, not sure if it’s anamolous or the -nopic severity. But I usually fail all those tests, miserably. Colors I get mixed up with range from blue and purple, to orange and green, to brown and red or brown and black and commonly brown and green. It’s those browns and purples that mess me up thd most. Luckily I’ve only had one experience in school where my deficiency affected me. But usually I can’t distinguish blue from purple. And I’ve accidentally colored things like the sky purple in like art class when I was in elementary school. But I’m not exactly sure if I have enhanced night vision or not. I haven’t really tested it out or noticed. As for camouflage, again I haven’t tested to see if I could see the object with camo or not. But I’m sure I could. Well I’m glad to read these articles though, because I get to relate to others with the same disability and plus it’s really interesting, so that’s awesome.
J. Glenny; December 30, 2010 at 9:08 pm
Re:- Colour perception-v-night vision.
I have slight deutan deficiency, not notieable for practical purposes but would fail the Ishihara test, though not the Farnsworth S15, for what it is worth.
However, my night vision is definitely better than average. When navigating at night or viewing the night sky, it takes much less time to become accustomed to darkness, only a minute or so; not the usual twenty minutes or more. Also, the customary use of averted vision in these circumstances makes no noticeable difference. When walking at night in a group and on many other occasions, it was apparent that I was able to see clearly obstacles that others could not see at all. Except in a totally enclosed space, such as a room with no windows, it is never so dark that I can see nothing.
Experts always seem reluctant to acknowledge this colour to night vision relationship, on the grounds of lack of evidence; indeed, any mention of the subject is usually met with silence. Could this be a reluctance to accept that a condition normally regarded as a deficiency actually embodies a sizeable benefit? Where would this leave the condition of ‘normal’ colour vision?
It seems likely that this is an evolutionary legacy from early mammals, which were nocturnal and had a greater requirement for night vision than colour vision.
Perhaps it is time for objective night vision tests to be devised, and conducted as matter of course, in conjunction with colour vision tests.
jim; December 9, 2010 at 3:56 pm
I am only mildly color deficient. i have relay trouble with light green light pink (see them as grey of can not tell then apart) dark green dark red (see them as black). i have good night vision but i rock at hunting. I always spot game faster than color normal friends and family. camo is less effective on my one of my students found every person in that camo commercial instantly (he also failed the color plate test). this hunting advantage could be why this is genetic issue is so common is humans.
Bill Kozak; November 7, 2010 at 9:41 pm
I see 70 on the plate where I should see a 29 for the link about the ishihara test. I’ve since done some searches and it’s the same with this color blindness test and this one where I can’t see anything on plate 13. I have never been diagnosed for this before, but I wonder how accurate these things are. I’m certainly going to bring it up to my GP. It seems like this is a test you can get from amazon too, though it’s expensive. Thanks for this article.
Bluedreamer; November 4, 2010 at 9:03 pm
Another colour blind web dev here, red/green/brown is hard for me as is anything in the blue/purple/violet range.
I was interested to see some people mention that c/b people have better night time eyesight. I’ve can vouch for that as I’ve had plenty of times where I could distinguish certain features at night when normal sighted friends couldn’t. Don’t really know why, it just is that way. I guess it might be because my eyes aren’t distracted by all those darn colours!
Back to the web, the one thing that developers can do is *always* underline text links (with the excpetion of “obvious” link blocks such as main navigation). That way you can get away with using more similar text/link colours and not worry about it too much. Unfortunately removing them is all too common, along with not styling :focus links but that’s another story.
Nixar; October 30, 2010 at 9:23 am
Not experimental evidence, but it’s commonly thought that early mammals lost most of their color vision because they were nocturnal. It was regained only very recently: we humans only share this capability with apes and old world monkeys.
Joe Dolson; October 29, 2010 at 2:49 pm
Well, this is certainly very interesting! I’m glad that this article has spawned this discussion. Although I’m still not certain that this constitutes proof positive that people with color vision deficiencies have improved night vision, there’s no question that it’s a very common thread of personal experience — which points in the direction of truth, at any rate!
Thanks for all your responses!
Vivek R; October 29, 2010 at 12:31 pm
I am color blind (fail 3 on the test) and my wife is not. We have frequent power outages at night and I am the first to find the lighter / candles. She’d have no clue they were where I picked them up from. I wear glasses too (shortsighted) but she has perfect vision. This is the first time I am reading about others who experience this.
Loren Pechtel; October 29, 2010 at 11:49 am
I will definitely agree with color vision problems and camouflage, although my understanding is that the military has figured out how to make camouflage that works against those with color problems also. I have some red-green weakness and I think I was like 12 or 13 before I understood what camouflage was supposed to be–most every example of it I saw stood out like a sore thumb to me.
Just because it blends in well for someone with normal color vision doesn’t mean it blends in with abnormal color vision.
ColoUr Blind Pete; October 29, 2010 at 10:12 am
I’m colour blind, in the sense that i can’t tell the difference between brown, red and green. i can sometimes make correct intelligent (or so i think!) guesses. However I really do see better at night than my girlfriend for example. It’s little consolation for not fully enjoying the full spectrum of colour nature provides, but at least if i get stuck down a mine it might help!
crazybat; October 28, 2010 at 12:21 pm
I must say that I’ve never heard about colour blindness and having better night vision. Interesting.
It would also be interesting to see if there’s a correlation between the severity of colour blindness to more effective night vision. Get snopes on the case 🙂
I personally fail in only one circle on the Ishihara test (the 6). I do know that my eyes adjust quite quickly to the dark. As well, I’ve never had a problem driving at night time.
Stephani Roberts; October 28, 2010 at 12:05 pm
@Matthew My husband is color blind and he was able to spot deer in the fields last weekend as we drove home at twilight. They were almost invisible to me as they blended into their background but he saw them easily as distinct shapes. He speculated that it was a result of his color blindness. I think so. There are advantages, this could correlate with sharp shooting. He mentioned that color blind men were put at the front of the lines because they were able to spot camouflage. Here’s a short article about the upside of color blindness: http://discovermagazine.com/2007/apr/the-upside-of-color-blindness
marlene frykman; October 28, 2010 at 11:16 am
@joe: wonderful. that is a fantastic tool. thanks for sharing!
Joe Dolson; October 28, 2010 at 11:09 am
@marlene Thanks for the tip! I’ve fixed the link.
marlene frykman; October 28, 2010 at 8:31 am
hi joe, just letting you know the link to the vision simulator is broken 🙁
Joe Dolson; October 26, 2010 at 12:55 pm
@Matthew I’ve read that as well; but again, without any definitive evidence.
@Karl What I wonder about that is whether that perception is because you’re more accustomed to identifying what you can see with reduced color or because you can actually see better. Given that one of the characteristics of low-light conditions is a significant reduction of color definition, I’m wondering whether the real issue is in the ability to understand what you’re seeing, rather than actually having improved perception in low-light conditions. From a subjective perspective, this may give you better understanding of your surroundings in low-light, but not actually mean that you have better vision. Does that make sense?
Karl Groves; October 26, 2010 at 12:20 pm
re: Night Vision. I have no evidence, but I am very color blind (as in usually can’t get any of the items in the Ishihara tests) and I seem to have much better night vision than most people.
Bryan; October 25, 2010 at 10:01 pm
Thanks for clearing things out. Very good and interesting read.
Matthew; October 25, 2010 at 4:15 pm
I’ve heard a similar rumor that colorblind individuals are better sharpshooters, with the justification being that your retina packs in more rods, which give you a higher resolution image. I’d like to see the Snopes on that one (although I still like to repeat it 🙂 )