Last year when we made rainbow cupcakes, I started with a scratch recipe white cake batter. This year, because I never know if Baby is asleep for two minutes or two hours, I went the faster route.
From there, it's pretty simple.
I divided the batter into six bowls and added food coloring to each.
The Girl was my official color mixer.
Next, starting with red, I layered them in my pan.
Bake according to package directions.
Once it has cooled about 10 minutes, remove from pan.
You could frost it at this point, but we had ours with rattle can whipped cream.