Color Oracle

[ravells]

is a natty bit of software for testing what your maps (and other designs) look like to people who have various forms of colour blindness.

You can get it here.

[Fransie]

In my opinion (or, for my degree of colour blindness), the simulation is very extreme, way too strong.

I personally prefer the Photoshop plugin here. I used it to explain my colour blindness to my wife. Apply the filter, then if neccesary Fade it (ctrl-shift-F) until the colourblind person cannot see a difference between the original and the filtered image. My wife was adamant that the before and after pictures (of a bunch of red roses) were very much different.