accessiBe - Making websites accessible to people with disabilities

Colorblind - Dalton - Software for colorblind people. Dalton is software allowing people with different kinds of color blindness (colour vision deficiency) to see more colors.

Sim Daltonism - From the perspective of a color blind person, some colors are impossible to distinguish.

Free Color Picker - An advanced color picker, screen magnifier and color palette manager

Coblis - If you are not suffering from a color vision deficiency it is very hard to imagine how it looks...

Color Oracle - Color Oracle is a colorblindness simulator for Window, Mac and Linux.