help!

please excuse the poor image quality, and the fact that this is far from done... I am entering a playbill cover contest for Carnegie Hall. The theme is "musical journeys". I'm doing the piece in black and white, but I want to digitally color it. How do I do that?? Is it possible in photoshop to lock the black part and color underneath it? I don't want to have to individually color each cell. Please let me know, thanks for the help :)