It was actually easier than I expected. I have scratch recipes for cakes that are allergy friendly for him, and they only yield a dozen cupcakes, so I made a whole batch of vanilla, and a half batch of chocolate. The batch of vanilla I separated and made one portion green so I could get the three colors.
Then it was just a matter of dribbling the colored cake batter into the cupcake liners, and voila!
Happy Birthday Boy enjoying a second cupcake!