Preheat oven to 350 degrees, then lightly spray or line cupcake pans and set aside.

Mix cake mix, oil, water, and eggs together with electric mixer for approximately 2 minutes.

As best as you can, try to evenly divide the batter amongst six, small bowls.

Using a toothpick, use small amounts of Wilton gel food coloring at a time until you achieve your desired color.

This is the tricky part. Once all batters are colored to your liking, begin evenly distributing your batter among the prepared cupcake pans.

Continue dividing the batter in the order you want your rainbow to appear.

Bake for 15-18 minutes and allow to cool completely.

While cupcakes are cooling, prepare the frosting by mixing all ingredients together using an electric mixer.

Frost your cupcakes as desired and served. I used a Wilton 5 tip on the cupcakes in the front of the picture and a Wilton 1M tip on the back cupcakes.