I've had the opportunity to design a set of characters and make song and instrument illustrations for the music game Know Note. The game currently has 40 well known songs you can play in various difficulties. You can check out the game, currently in beta, at http://www.knownote.com
We did character designs mostly focusing on outfits and base colours, as well as illustrations of them playing instruments and dancing. We went with an ethnically diverse group which, if it were up to us, would've been much bigger.
The other three had less established colours and I tried out various schemes.
In total, 40 song images were needed as well for songs like Kryptonite, Life is a Highway, Yellow, Oops I did it Again, Little Lion Man, Ironic etc.