I have a huge list of bathtub paint recipes saved up, but the other day I needed something to entice Monkey into the tub so I went the easy route. Dollar store shaving cream and food coloring.
I always keep a stash of cheap shaving cream because it's useful for lots of messy projects. It makes great stocking stuffers!
I just filled up some plastic bowls with shaving cream and added some food coloring. At the time all we had was blue and yellow. It has been a fun way to teach the boys about mixing colors too.
He had a blast painting the bathtub and when he was done I just sprayed everything down with water. Easy cleanup.