Begin by adding ⅓ cup cornstarch and ⅓ cup baking soda to a medium sized bowl. Slowly add ½ cup water to the bowl, and mix well with a small whisk. Mix until there are no lumps, and the mixture is somewhat thin and pourable. If your mixture seems too thick, add a little bit more water, but be careful not to add too much, or your chalk paint will be too runny.
Next using the funnel, pour the cornstarch/baking soda mixture into a clear squirt bottle.
Add 5-6 drops of the food coloring of your choice, or mix a couple colors to create a new color. Put the lid with the cap back on the squirt bottle, and shake very well. If the paint color is not dark enough, add more food coloring. This process can get pretty messy, so make sure you are wearing clothes you are comfortable possibly staining.
Test your paint on a sidewalk/driveway. If the paint comes out too quickly and runny, you may need to add more cornstarch and baking soda. If it is too thick and hard to squirt, you may need to add slightly more water.