Draggable Masks

I’m trying to create three circles on the stage, one red one green, one blue. When Red overlaps blue, I want the overlapped area to be magenta. When blue overlaps green, the overlapped area should by Cyan. When red&green, it should be yellow, and when all 3 mix it should be white.

How do I create the color effect. Right now I have the overlap constraints working and a simple TRACE outputting the color. I need to know how to create the color effect when they mix.

You could try to set the alpha to 50, for instance. But what does it have to do with draggable masks?

pom :-\