Mix the salt, flour and food coloring together, adding just a few drops of water at a time to moisten. You want to keep the mixture thick, but not so thick that you can't spread it on the paper. You will need to experiment a bit to reach the right consistency. Repeat the same recipe in different bowls for each color you would like to use. Use the mixture to paint on plain white paper with brushes or Q-Tips. Encourage your little artists to use ample amounts of paint in their creations because more paint will end up producing a "puffier" finished product. When finished, put the piece of paper into the microwave for 20-45 seconds until it bubbles and dries. An adult should remove the paper from the microwave in case the paper or paint is warm. Keep the artwork flat for a few minutes until it dries completely.