CO A rhythm of rainbow-osity. It'll work better if it's not cold. Put the milk in a cup. Add drops of food coloring in a triangle or square pattern Put a drop of soap in the middle of the food coloring design and watch the colors move.
Milk has fat in it and the soap breaks up the fat.
The food coloring swirls into the places where the fat used to be. Now, instead of using milk, try it with glue. Soap also prevents glue from sticking together. If you let the glue harden, you can cut away the cup and you have a colored disk. It was a great science experiment.