Cupcakes should be two things: edible and pretty. These rainbow cupcake fulfill both of those requirements. The cupcakes themselves are made from a simple vanilla batter (although you can use chocolate if you so desire.) Once they are baked and frosted with vanilla buttercream, the fun begins. Fill small spray bottles with food coloring (one color per bottle) and spray on top of the frosting. You’ll end up with a pretty (and tasty) rainbow!