People are always wondering what i see when I tell them I'm a bit color blind. My reds and greens tend to mesh together as well as purple/blue. I don't know what it is, I've never really had it diagnosed.
But this site allows you to see what other people don't see. It's basically a color palette chooser for web designers and gives you an idea of what various degrees of color blindness will do to a color you choose for a design.