1. Use a box of white cake mix and make as directed.
2. Divide the cake batter into 6 bowls, evenly and add food coloring. (For an exact on the food coloring, visit the Family Fun link above.)
3. Put the cake batter into the cupcake cups, starting with purple and begin layering the colors. Purple, blue, green, yellow, orange and red. This does take some time to do this to each of the cupcakes, so if you are short on time, make a rainbow cake instead of the cupcakes.