Java GUI animation problem?

I have a frame containing five draw panels. Each panel has a rectangle box that moves from top to bottom. Simple animation. (I am actually trying to simulate the go-back-N ARQ). So anyway, as each rectangle reaches the bottom, is there a way I could have a rectangle (of different color) trace back the path the original one followed down. In other words, if a rectangle of color red comes down, I want a rectangle to color green to go up on the same path. Thanks a bunch.