Measure the flour into a saucepan and slowly add water. Use a wooden spoon to continuously stir and keep the mixture from clumping.
Place the mixture on the stove on low heat. Continue stirring, and add water as needed to thin the flour mixture and keep the consistency uniform.
Remove the flour mixture from the heat and pour it into 3 or 4 small bowls. Add 2 to 3 tablespoons of liquid tempera paint to each bowel in the colors you desire.
Stir each mixture until it is smooth and has an even texture. If the paint mixture is too thin, add a small amount of flour or cornstarch to it. If the paint is too thick, stir in a few drops of water at a time.
Finish each face-paint color by adding a few drops of liquid starch to make it a matte, opaque face-paint color. Alternatively add a few drops of liquid detergent to make it a glossy, slightly transparent color. However, these are not needed.