Mix cornstarch and water to make clumps disappear. Mix in paint and dish soap. Pour it into your spray bottle and shake well. Repeat for however many colors/bottles you want!
Spray paint your driveway and sidewalks! Spray with a hose to remove.
Recipe Notes
Note: the cornstarch will settle to the bottom of the bottles if you let them sit. So either have one awesome spray-painting extravaganza and use up all the paint, or plan to do a lot of shaking the next time you try to use them.