One of the best books I have seen on breeding for color varieties is \" Old English Game Bantams as Raised and Bred in the US\" by Fred Jeffries. Old English Bantams come in about 40 different color varieties so they have a lot of experience making different colors.
Kids are naturally curious and want to try something different or special. I have told kids in our local 4H club to get one variety to try and win with (Black Old English, Black Cochin, Rhode Island Red, etc) and then one to play with and try to develop or improve. My daughter has Black Cochins that she hopes to win with and she has some Golden Laced Cochins that she is trying to improve by crossing to the blacks and then selecting for color and type.
The kids could also get involved with a project to get a new breed or variety into the standard. I know of several, Lavendar Ameraucanas, Blue Jersey Giants, Marans to name a few. This would give them a chance to work on something new while working with other breeders. They would also have a better chance to find someone to take over their project when they decide to give up on 4H and go off to college or chase girls or what ever else kids decide to do.