We made rainbow cupcakes the other day and they turned out awesome. I started with a traditional boxed cake batter and divided it into 6 bowls. Add food coloring to each bowl. Then we scooped 1 scoop of each color into a muffin tin. My cupcakes turned out very, very full. Almost a little too full. After they baked I added a buttercream icing and a few green sprinkles. Tada! They were tasty and very pretty to look at.