Set out a 3-ounce plastic cup, or other disposable container, for each color you want to make. Put about 1 tablespoon of liquid glue in each container. For each color, add one or two drops of food coloring to a container. Stir with a disposable coffee stirrer, toothpick or similar item until thoroughly mixed. Stir smoothly to keep the glue free of bubbles. If the paint seems too thick, add one or two drops of liquid dish soap and stir. For deeper colors, add more food coloring one drop at a time, stirring after each drop.