Applied Color Theory- Colorblindness

From: Dan Margulis, INTERNET:76270.1033@compuserve.com
Date: Tue, Jan 4, 2000, 5:57 PM
RE: Colorblindness and the Web

Folks,

Here's a problem that you should keep in mind when designing web pages, since the color-blind represent a significant percentage of the population. Here's a note I recently got from a professor at a university outside the United States. I've posted my reply separately.

Note: in many countries color-blindness is referred to as Daltonism, as it is in this correspondence.

Dan,

So what can this student see? Do green and red backgrounds on a Web site become invisible to him? I thought that daltonics could see blocks of color as shades of gray or brown or something. Thus,according to http://www.lighthouse.org/color_contrast.htm , designing colorblindness-accessible Web pages should simply be a matter of paying attention to the contrast of hue, lightness, and saturation in font and background colors.

-----Original Message-----

>Hi! My name is -------, student number 123-456-7890, I'm in your
>"----------------" class.

>I just visited your website, and I have a petition for you. I'm a
>"daltonic" person, which means that I don't recognize or SEE some
>colors... Can you please CHANGE the background green color of your
>pages??? Or use only color schemes that doesn't have green or red?
>The only color that I can see is blue, but only if it is by itself
>illustrated, not in combination with other colors...

>Thanks for your help.


From: Dan Margulis, INTERNET:76270.1033@compuserve.com
Date: Tue, Jan 4, 2000, 6:40 PM

<<So what can this student see? Do green and red backgrounds on a Web site become invisible to him? I thought that daltonics could see blocks of color as shades of gray or brown or something.>>

Exactly, but he sees green and red as the same shade of gray, so he can't read red type on a green background.

<<Thus, according to http://www.lighthouse.org/color_contrast.htm , designing colorblindness-accessible Web pages should simply be a matter of paying attention to the contrast of hue, lightness, and saturation in font and background colors.>>

No, lightness is the only part that counts. For a truly color-blind man (there are essentially no color-blind women), there is no perception of hue and saturation at all. So, if you put red type on a yellow background, it will be legible, because the type is darker than the background, even though he won't see a hue or saturation difference.

To go a little deeper, daltonismo varies across two opponent-color axes, red-green and yellow-blue. One can have reasonably good perception of one axis and nothing in the other. However, your guy is the most typical: totally void of red-green perception, deficient in yellow-blue but not completely blind to it. He probably won't see light yellows as anything other than white, but a brilliant yellow he will take to be an anti-blue, in other words, a brown.

I've had two people like this in my classes and have taught them to color-correct by the numbers. But it's hard to believe how complete the failure to perceive red and green is. I have a picture of a forest which has a red maple in the middle of it, leaves purplish-red in the middle of an ocean of green, and these guys can't see a difference even when I point out the specific tree to them.

In short, if you avoid contrasts between red and green, you'll solve most problems. If you have contrasts between red and blue, now and then some daltonistas will have trouble with that too. Yellow usually is OK because it's so much lighter than the other colors.

Or, a better way of thinking: imagine what your page would look like if it were in black and white. If you think certain parts of it won't have contrast, that's what a daltonista would think, too.


From: Lee Blevins, INTERNET:leeb@ids.net
Date: Tue, Jan 4, 2000, 7:33 PM

Very interesting.

I have two cousins who see only in black and white. I belive it's very hereditary since their father was the same.

Myself, I see everything in cmyk. Every color I come in contact with is instantly broken down in my brain as amounts of cmyk. Is there a name for this ailment? Have I worked in the printing business too long?


From: Dan Margulis, INTERNET:76270.1033@compuserve.com
Date: Wed, Jan 5, 2000, 12:02 PM

Lee writes:

<<I belive it's very hereditary since their father was the same.>>

Nope. Colorblindness, like hemophilia and (some say) extraordinary mathematical ability, is sex-related recessive, the translation of which is, only men get it, and it is passed through the *mother.*

<<Every color I come in contact with is instanly broken down in my brain as amounts of cmyk. Is there a name for this ailment?>>
<<Have I worked in the printing business too long?>>

For even while I dwell in darkness and in silence, in my memory I can produce colors, if I will, and discern betwixt black and white, and what others I will: nor yet do sounds break in and disturb the image drawn in by my eyes, which I am reviewing, though they are also there, lying dormant, and laid up, as it were, apart. For these too I call for, and forthwith they appear. And though my tongue be still, and my throat mute, so can I sing as much as I will; nor do those images of colors, which notwithstanding be there, intrude themselves and interrupt, when another story is called for, which flowed in by the ears. So the other things, piled in and up by the other senses, I recall at my pleasure. Yea, I discern the breath of lilies from violets, though smelling nothing; and I prefer honey to sweet wine, smooth before rugged, at the time neither tasting nor handling, but remembering only.

--St. Augustine
--Tenth book of confessions


From: INTERNET:mact@adcomgraphics.com, INTERNET:mact@adcomgraphics.com
Date: Wed, Jan 5, 2000, 12:42 P

<<For even while I dwell in darkness and in silence, in my memory I can produce colors, if I will, and discern betwixt black and white, and what others >>

Do you have all of these in your mind, evoking them at will, or in some PDA notebook, or ?
That's one of the most notable parts of your articles, the quotations (and sometimes the illustrations) you use.


From: Dan Margulis, INTERNET:76270.1033@compuserve.com
Date: Wed, Jan 5, 2000, 7:32 PM

Mac writes:


<<Do you have all of these in your mind, evoking them at will, or in some PDA notebook, or ?>>

I had extra RAM hardwired into my brain some time ago. A lot of color stuff I do have filed away, kind of like the files Ron posted. You never can tell when you'll need it. I used that St. Augustine quote on my Xmas card several years back.


From: INTERNET:mact@adcomgraphics.com, INTERNET:mact@adcomgraphics.com
Date: Wed, Jan 5, 2000, 8:50 PM

<<I had extra RAM hardwired into my brain some time ago. >

Well, let's hope it does not grow DIMM! you visiting MacWorld this week?

Mac Townsend,
Adcom Graphics, Fairfield, CA:
www.adcomgraphics.com
A Corel Platinum Service Bureau


From: Dave Adams, INTERNET:david.a.adams@kodak.com
Date: Thu, Jan 6, 2000, 9:15 AM

Dan Margulis wrote:

> Lee writes:

> <<I belive it's very hereditary since their father was the same.>>

> Nope. Colorblindness, like hemophilia and (some say) extraordinary
> mathematical ability, is sex-related recessive, the translation of which
> is, only men get it, and it is passed through the *mother.*>>

Dan, I have to disagree with your statement "ONLY MEN GET IT". I imagine most statisticians would see the numbers as insignificant. Stats I have seen numbers are something like 1 of every 10 men vs 1 of every 200 women. But I know 2 women who have different degrees of color blindness, so they might take exception of your statement as well. <G>

BTW, enjoying the great dialogues and info being passed on.


From: Michael Stokes, INTERNET:mistokes@Exchange.Microsoft.com
Date: Thu, Jan 6, 2000, 1:10 PM

OK, quoting from Wyszecki and Stiles' Color Science: Concepts and Methods,
Quantitative Data and Formulae (second edition)
p464

Salient Properties of Color Defectives

1. Protanomalous
Color discrimination through the spectrum is materially reduced from red to yellowish-green but to a varying degree in different cases (540nm peak) 1.0 percent among males, 0.02 percent among females

2. Deuteranomalous
Color discrimination through the spectrum is materially reduced from red to yellowish-green but to a varying degree in different cases (560nm peak) 4.9 percent among males, 0.38 percent among females

3. Protanope
Color discrimination through the spectrum is absent from the red to about 520nm 1.0 percent among males, 0.02 percent among females

4. Deuteranope
Color discrimination through the spectrum is absent from the red to about 530nm 1.1 percent among males, 0.01 percent among females

5. Tritanope
Color discrimination through the spectrum is absent from the greenish-blue to blue (445 to 480nm) 0.002 percent among males and 0.001 percent among females

6. Rod-Monochromat
No color discrimination 0.003 percent among males and 0.002 percent among females. So, that's a total of 8.005 percent among males and 0.433 percent among females.

I'd say Dan's comment "(there are essentially no color-blind women)" is "close" to correct ;)


From: Dan Margulis, INTERNET:76270.1033@compuserve.com
Date: Thu, Jan 6, 2000, 1:25 PM

Dave Adams writes:

<<Dan, I have to disagree with your statement "ONLY MEN GET IT". Iimagine most statisticians would see the numbers as insignificant. Stats I have seen numbers are something like 1 of every 10 men vs 1 of every 200 women.>>

Well, those numbers are definitely screwed up. True daltonics aren't 1 in 10 among males, but even if they were, there would be 1 in 100 women, not 1 in 200. The numbers you are quoting may be those with a color deficiency, but not what most people would consider colorblind. (I don't know what the textbook definition of colorblindness is; mine would be someone who can't tell a red from a green of the same luminosity, or someone who can't tell a yellow from a blue of the same luminosity.)

My guess is that true daltonism is found maybe in 1 of every 100 men, which would mean one of every 10,000 women.I didn't mean to suggest that women can't theoretically be colorblind; it's just that they're, as you say, an insignificant percentage of the colorblind population generally. If there's a person in the lobby who's colorblind, and if my numbers are correct, the odds are a 100-1 that that person is male.

Technical explanation for lurkers: most human characteristics are determined by a combination of genetic information received from the parents. Some characteristics are recessive, for example blue eyes. A person cannot be blue-eyed unless *both* parents contribute the appropriate gene. If either one contributes a brown gene, the child has brown eyes (but may carry a blue gene that could be passed on to children).

The color of the eyes has nothing to do with sex, but colorblindness does. Like blue eyes, it is recessive, which means you have to get it from *both* parents--but only if you happen to be a woman. This is because colorblindness is governed by the same set of chromosomes that determine gender. These are commonly called the X and Y chromosomes; a woman is XX, a man is XY.

On the Y chromosome that causes one to be male, the colorblindness information is missing altogether. Everything therefore depends on what is found in the X, and if it is the bad gene, men are SOL. Women, OTOH, aren't colorblind unless *both* of their Xs have the problem. This means that, for something like hemophilia, which is also sex-related recessive, if men have a 1 in 50,000 shot of getting it, women have a 1 in 2,500,000,000 shot.

These undesirable traits are always passed through the mother, because a man always gets the blank Y chromosome from his father. This is why Queen Victoria, who didn't have hemophilia herself, but carried the gene, became indirectly responsible for the high incidence of hemophilia among male royalty in Europe.


From: "Ron Bean", INTERNET:rbean@execpc.com
Date: Thu, Jan 6, 2000, 8:52 PM

 

Dan Margulis <76270.1033@compuserve.com> writes:

>My guess is that true daltonism is found maybe in 1 of every 100 men, which
>would mean one of every 10,000 women.

A long time ago, I heard that there are a few people who can actually see four primary colors. That is, their eyes have four types of color receptors, not three. The percentage of the population was said to be similar to the number of women who are colorblind (ie, very small). I don't know if they could see a larger part of the spectrum, or just the same spectrum broken up differently. Have you ever heard about this?


From: Chris Murphy, INTERNET:lists@colorremedies.com
Date: Thu, Jan 6, 2000, 9:06 PM

>A long time ago, I heard that there are a few people who can
>actually see four primary colors.
>Have you ever heard about this?

I have never heard about this with a small percentage of the population. In fact it's MOST of the population except possibly those with color discrimination problems. The fourth "primary" is yellow. It's not really a primary in that the human eye is sensitive to yellow, it's that it's very sensitive to the total lack of blue light. So if the eye sees no blue light, we perceive it as though it's a primary (a color that doesn't have any further components, or breakdown).


From: "Ron Bean", INTERNET:rbean@execpc.com
Date: Fri, Jan 7, 2000, 8:17 PM

Chris Murphy <lists@colorremedies.com> writes:

>>A long time ago, I heard that there are a few people who can
>>actually see four primary colors
>>Have you ever heard about this?
>I have never heard about this with a small percentage of the population.
>In fact it's MOST of the population except possibly those with color
>discrimination problems. The fourth "primary" is yellow.

I've heard that also. But what I'm talking about was definitely genetic. The people investigating it were biologists. I think they said some bees have it also. I don't remember if they had conclusive evidence yet, or if they were still investigating. It was quite a few years ago, and I never heard anything more about it.


From: Chris Murphy, INTERNET:lists@colorremedies.com
Date: Sat, Jan 8, 2000, 2:53 AM

>I've heard that also. But what I'm talking about was definitely
>genetic. The people investigating it were biologists.
>I think they said some bees have it also.

Well it turns out that red, green, and blue aren't the exact primaries either as the wavelengths are short, medium-long, and long. Those don't correspond exactly to blue, green, and red respectively anyway - so I don't see why they would say that it does corrrespond exactly to yellow and not yellow-orange, or yellow- green, or red-orange.

But in any event, you're saying they have four different kinds of cones instead of three.


From: "Ron Bean", INTERNET:rbean@execpc.com
Date: Sun, Jan 9, 2000, 12:35 PM

>>I've heard that also. But what I'm talking about was definitely
>>genetic. The people investigating it were biologists.

>Well it turns out that red, green, and blue aren't the exact primaries
>either as the wavelengths are short, medium-long, and long. Those don't
>correspond exactly to blue, green, and red respectively anyway - so I
>don't see why they would say that it does corrrespond exactly to yellow
>and not yellow-orange, or yellow- green, or red-orange.

They didn't say that. (Sorry, I didn't mean to link the two ideas-- I just meant that I'd heard elsewhere that yellow is
considered a "perceptual primary", but that doesn't have anything to do with this).

>But in any event, you're saying they have four different kinds of cones
>instead of three.

Yes. But I don't remember if they said what the fourth color was (might have been near-UV). That's why I was hoping someone else had heard of it. It's possible that they weren't able to prove it, or that nobody else thought it was important because it's so rare.

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