This is an experiment perfect for a rainy day...and you have everything you need right in your cupboards.
a "deep" plate-suitable to hold milk
Pour milk onto the plate and then add 3 drops of 3 different colors of food coloring to the center of the plate of milk.
Dip the end of a q-tip into the detergent.
Place the q-tip into the center of the food coloring and watch the magic.
The colors swirl and twirl and mix together creating a rainbow of colors.
And it also contains a science lesson about surface tension.