A small free tool for OS X I found useful is Sim Daltonism[1]
Sim Daltonism is a color blindness simulator for Mac OS X. It filters in real-time the area around the mouse pointer and displays the result ” as seen by a color blind person ” in a floating palette.
If anybody has information about how people with limited color vision perceive the aesthetical side of colors (e.g. how well colors go together in a web site palette) I would love to read about it.