Drosphilia researchers have a leg up on web designers.
Well, at least they've got a decent explanation of colorblindness. A short paper on colorblind audiences was written a few years ago for researchers presenting their findings on the very latest in the world of flies. The guidelines are easy to understand, and the changes are easy to incorporate.
Here's a bit:
"There are always colorblind people among the audience and readers. There should be more than TEN colorblinds in a room with 250 people. (50% male and 50% female) There is a good chance that the paper you submit may go to colorblind reviewers. Supposing that your paper will be reviewed by three white males (which is not unlikely considering the current population in science), the probability that at least one of them is colorblind is whopping 22%! ... When preparing your presentations (papers, slides, web pages etc.), please take this into account. Here are some comments on how to make figures and presentations colorblind friendly.
I would also recommend a quick look at the Ishihara test for colorblindness for a shot-in-the arm understanding.
And while you're on a colorblindness kick, you'll lose blogger points if you don't read at least Day 12 of the Dive Into Accessibility website, which is the best online introduction to making your website+blog readable by everyone, except illiterates, period.