My father is color blind and given that I work in games where the visuals are important, I've always wanted to write a filter for screen shots (or even some type of shader) that emulated different forms of color blindness.
I've seen plenty of references but never have been able to track down algorithms.
Any algorithms would be appreciated.
Can't help you on algorithms, but the following article was quite an eye-opener (excuse the pun): http://critiquewall.com/2007/12/10/blindness.
Ah, actually, http://www.vischeck.com/ is useful.
Google came up with a number of links, perhaps one provides source or algorithm descriptions: http://www.google.com/search?hl=en&q=simulating+color+blindness&aq=f&oq=
Edit: Thanks Torlack for pointing out that everybody knows about Google. But using Google effectively requires using the proper search terms, and good search terms aren't always obvious. Judging by the returned page titles and a couple of the links, this particular search seemed highly relevant. I don't think it was a bad enough answer for a downvote.
My Google search came up with this one, which appears to be exactly what you're looking for. Eight different versions of color blindness are simulated by multiplying each of the R,G,B values by 3 different percentages and adding them together.
The colorjack link has good info, but I use http://colorfilter.wickline.org/. It can check a whole page: images, CSS colors and all.
I came across Color Oracle and thought it might help. Here is the short description:
Color Oracle is a colorblindness simulator for Windows, Mac and Linux. It takes the guesswork out of designing for color blindness by showing you in real time what people with common color vision impairments will see.