All it required was shaving cream, food coloring, a muffin tin, and a brush (I used an old basting brush).
Then I put the toddler the tub, and let him paint his little heart out. He had a blast.
The best part about this is the easy clean up! Rinse the shaving cream off of your bathtub (and walls) with a cup of water! Ta-Dah! Done. And then throw your kid in the bath to finish up. And then bed. That's my favorite part. :)