Place about ¼ cup potable water each into small bowls. Add 5 or more drops of food coloring to each bowl. Mix well.
Test the color intensity of the water by painting on plain white paper. If you want the color to be more intense, add a few more drops of food coloring until you achieve the desired color.
Put the colored water into the sections of an ice cube tray.
As a color learning and mixing activity, just prepare three colored water solutions in Step 1, the primary colors—red, yellow and blue. Spoon in the colors into each tray section by pairs to come up with the secondary colors—orange (yellow + red), green (yellow + blue), and purple (blue + red).