XOB:
This picture shows an example of the additive color mixing. The most striking example of this I ever saw was in the Hard Rock Casino in Las Vegas. There was a white wall with some cast metal letters mounted on it and the letters all had shadows of different colors. It just about drove me crazy. My poor brain was trying to reconcile the proper shape and angle and area for all the shadows with the obvious problem that they were not "dark". This image recreates the effect as well as any simple 2d picture can.
Here is the link for the science behind the image.
http://www.newtrier.k12.il.us/academ...t/coloshad.htm
EDIT: I found a picture and an explanation I like better.
http://www.exo.net/~pauld/summer_ins...ploration.html