Hmm. I wasn't sure what to call this little project. White crayon under watercolors seemed a bit stupid, yes? I'm pretty sure I remember doing this one in elementary school art class.
At any rate, this is an easy little art project to have in your pocket for those times the kids want something to do. It's not rocket science, and you already have the stuff around. Bean and Short Pants drew on watercolor paper with white crayon, and then painted over them and watched their drawings appear. The key is to press hard with the crayon. Short Pants had fun with this one, but Bean *really* loved it. She actually ended up making two paintings as she didn't like the way her first came out.