We switched schools this year and our new school has a program where parents come in and teach art. It's pretty awesome for a state where art is not normally taught in elementary schools. My kindergartner came home with this amazing project last week and I had to share it. They used colored playdough to mix colors and create a color wheel.
It's so simple, so easy to do with a large group, and not remotely as messy as using paint.
(Sorry for the horrible picture quality, my daughter only let me have it long enough to snap a quick pic. :) )