RE the number of color-impaired I said
Papabaer said 5% to 8% based on his reading. Though I said this in my post, I should reiterate that this is 8% of males, not 8% of visitors.
Also, some people are synaesthetic (rare - between 1/2000 and 1/250,000) where they see text (about 70% of synasthetics) in color. My wife (a neuroscientist by the way) has a co-worker who is a synaesthetic and she reports that it becomes difficult for her to read if text is colored. For her every letter/word has a color and this is information she uses to read. When a word appears in the "wrong" color, it overrides her color perception and makes it hard to recognize, perhaps like a blue stop sign would be for us.
There was a recent study done on this where they created a random field of numbers in black and white and asked people to find all the 5s. Synaesthetics could do this something like 10 times faster than "normal" people because they searched by color, whereas people with normal vision needed to first identify the fives, then count them. This demonstrated that synaesthetic color perception takes place very early in neural pathway (i.e. *before* synaesthetics interpret the grapheme as a 5, they already see it in color).
Pages on synaesthesia:
My main job is as a sixteenth-century historian and I have to say there's a lot to be said for black on white, ink on paper. I walk into the archives, pull out a manuscript from 1539, and read it with no worries about hardware/software compatibilities.
There isn't even a word processor on the market that does footnotes well (if you really want it right, you need Quark or In Design), so I wouldn't hold my breath waiting for software aimed at a minority of people with relatively mild impairment.
The amazing thing to me is that nobody has done anything about traffic lights (as I mentioned before, you could add shape to color). This would actually save lives. I often need to stop at flashing yellow lights and get honked at by the people behind me, but I can't tell easily whether it's red or yellow. I'm just waiting for the day when some impatient person behind me doesn't realize I'm stopping and slams into me.