Here are some fun, artful ideas from around the web (and a cute photo of Daphne at the chalkboard because I couldn't resist):
Simple wooden rainbows at maya*made
Collaging with pretty, pretty papers at No Monsters in My Bed. I love Darcy's photos!
Super-sized string paintings at Let the Children Play
"Little Blue and Little Yellow"-inspired painting at Color Color Color
Interesting botanical paint at Paint Cut Paste