Painting...a First

Caedmon's actually done some finger painting before, at a friend's house. But this was a first for me. We didn't work at it for too long, but he had fun regardless. I have to work on not caring when he puts the paintbrush in one color and then directly into another, mixing them. I mean, he's a kid right?! Who cares...except when the colors get so mixed up that you can't tell which is which; how am I supposed to work on colors with him.... perhaps this isn't the best type of paint. What I'd really like to find is one of those water color books where you just paint with water and color shows up - now that's my kind of "mess!":)