Preheat oven and mix cake batter according to the box.
Once your cake batter is mixed, distribute the batter evenly among 6 plastic, disposable cups and grab 6 plastic forks.
Once the batter is evenly divided among the cups, color the first cup of batter red. Then, color the next cup of batter orange using more yellow coloring than red. Yellow next, then green, then blue, and then purple. For purple, you need to use an EVEN amount of blue and red food coloring. Otherwise, you end up with a nasty black color.
When that's done, take your cupcake pans (greased or prepared with cupcake liners), and pour a bit of red batter in each cup. Don't be too generous with the batter or you'll run out of it before you're done filling all of the cups.
Continue this strategy with all of the other colors. It's okay if each layer does not cover the next because they won't mix together; they will bake out evenly. Also, only fill the cups about 3/4 of the way full or the cupcakes will bake over the top.
Bake the cupcakes according to the instructions on the boxed cake mix. The cupcakes are done when you poke a toothpick through one of the cupcakes and it comes out clean. Let them cool and then frost with white icing. Enjoy!