This recipe cleaned up easily, but you might want to test it first on your grout.
1/2 cup body wash
5 tablespoons cornstarch
Mix the cornstarch with the soap. You may need to adjust the amount depending on your soap. Mix it in one tablespoon at a time. Divide mixture into smaller bowls. We used small containers with lids to save for future baths. Add a drop or two of food coloring to each bowl and stir.
Now it is time to paint...
walls, tub and faces!