Primaries with black and white would work fantastic as well! Get some yin and yang symbolism in there while we're at it. Possibly something where the black and white parts are the same (e.g. white shirt black pants) but the colored part is something different? (Someone gets a blue vest, someone else gets a red cape, etc.)

And yeah, feel free to lay on the symbolism as much or as little as you'd like. The gear ring works too, gears in general, since they all need to fit together (unite!!). Puzzle pieces as well-- perhaps everyone could choose their own motif of things that fit together?

Just some ideas to throw out there, obviously feel free to take it and run with it or not.