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That's along the lines I was thinking. The idea's going to be to combine colors to fill in a rainbow. The game will start out with a crushing thunderstorm which is gradually driven away as the player brings out the rainbow. It's not exactly grounded in hard science. =P
I'm thinking of a few possible mechanics, either dragging and dropping the circles together or clicking on them to send them skittering away in the opposite direction of the click. Maybe a "lens" could be used to redirect them.