To make this easy sidewalk/driveway paint, just mix equal parts cornstarch and water. The consistency will be watery. You don't want it too goopy. Then, add food coloring to make the colors you want. We used 3 drops per section of our muffin tin.
Ignore the messy muffin tin. I'm called Shaky Mommy for a reason. It's really a wonder I got this out of the house without spilling it! LOL. Aren't the colors pretty?