Vischeck has an absolutely amazing tool!
I’ve griped at Web developers forever about designing for the colorblind amongst us. “Please no red lettering on a black background,” I’d say. “Ja, ja, ja. I know you think it’s pretty, but a good percent of your users won’t be able to see your text, let alone read it.” They’d act like I was demented.
According to legalarts.com, “About eight percent of Caucasian males, five percent of Asiatic males, and three percent of males of other races are affected by dyschromatopsia. Only about a half-percent of females of any given race are affected.” That’s a good number of users who are affected by Web designers that don’t (or won’t) understand the situation.
Vischeck’s Web tool takes a given URL and returns a page that shows how the page would appear to someone with one of the three major types of color blindness – perfect for showing why-should-I-care designers where their oh-so-flashy sites will stumble. Great!
The site also has examples of how the colorblind see various images differently from the non-colorblind. Other information too.