Movie clip overlap colors

I am making a movie using AS for an intro flash movie. The movie includes rectangles that simply move downwards with random speed, height, and width.

My question is how I could change the color or alpha of the overlapping areas as seen in the quick sample I made and attached.

I have gotten some success from making the MC’s with an alpha and when they overlap there is a more solid color but it isn’t quite the effect I was looking for.

ummm look up setMask. ^.^ , if i get sum time ill make u up an FLA.

::EDIT::
there you go.

that is exactly what i wanted

except one thing, the movie i have has more than just two boxes. is there a way i can make it with more than two?