HELP!!!!!!!

I need to show a simple animation of the subtractive color interaction of 3 circles cyan,magenta,yellow respectively.....

exactly like this shockwave sample:
http://www.ontariosciencecentre.ca/s...btracting.html

Except I dont even need to let users move the circles..I will tween the movement myself...

The only way I can get the colors to interact like that is by making them somewhat transparent by lowering alpha... but then I lose color satuarion and that defeats the purpose of showing how these colors interact... (tri-hue effect)

PLEASE HELP ........