This is another GREAT idea from a friend of a friend! I love it! Hope you love it too!!
1/3 c. clear mild liquid dish detergent
1 Tbls cornstarch
Mix the liquid soap and the cornstarch together in a small bowl until blended. Pour the mixture, in equal parts, into several plastic containers (an ice tray works perfectly). Add 1-2 drops of food coloring to each container and mix with a small spoon.
This not only writes on the tub but also on your skin (just watch out for the eyes!) Not only will it get you clean, but your tub will shine!!