The color that consumes all other color. Showing urple in the light of day will cause all matter to turn to urple. The air, gravity. Needless to say, showing urple is pretty much as bad of an idea you can get.
Steve: Hey Guy, check out my Urple T-shirt.
Guy: No! You fool!
Steve & Guy: hjsdflkdhlkjhmnlkgtkjlgat,jklvf,jagkl;t,yjlvaBLEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEERG!!!!!"