Requires: Cake mix, food coloring and frosting... and maybe some sprinkles...
The internet loves rainbow cake and cupcakes, and for good reason! You get a surprisingly wonderful effect for remarkably little work. It's so easy that kids can do it (if they are old enough to spoon out ingredients without too much trouble) and so simple that the instructions barely need to be written out.
Theoretically, rainbow cake and rainbow cupcakes are best served at a kid's birthday party. But why stop there? I know plenty of adults who would squeal in delight to cut into a cake and find a rainbow. It's fun! Why not spice up the next office party with some rainbow color? Or you can be the star of the next potluck! Trust me: people will be talking about this cake. And it's so easy to make!
The functioning principle behind rainbow cake is that if you spoon cake batter carefully into a pan, it doesn't mix very much. If you have ever made marble cake, you know how well this works.
All you need is a box of white cake mix, whatever you need to make the cake mix (oil, usually, and some water), and a six-color assortment of food coloring. You will probably also want some frosting (white looks very nice) and maybe some sparkle or glitter sprinkles.
Step 1: Mix up your cake mix. Blend all the ingredients and what-not.
Step 2: Divide the cake mix evenly into six bowls.
Step 3: Dye each bowl a different color: red, orange, yellow, green, blue, and purple. Don't skimp on the food coloring here! A pastel rainbow cake will just make people sad. Remember that you can make orange out of red + yellow, green out of yellow + blue, and purple out of blue + red.
Step 4: Gently pour your cake mix into the pan, or spoon it into your cupcake tins. Preserve the real rainbow spectrum order for maximum visual impact. It's "Roy G. Biv," as in: red, orange, yellow, green, blue, violet (a.k.a. purple).
If you want to get technical about it, the spectrum should start with red on the top and purple on the bottom. If you are baking a cake in a pan, consider whether or not you will be flipping the cake over before you frost it, and adjust your color orders as necessary.
Step 5: Bake according to the directions. Let it cool, then frost and enjoy!