I had several comments and questions on this cake, so I wanted to share how fun and "easier than you think it was" to make.
First, I made one batch of cake batter using this yellow cake recipe. Next, I divided the batter into 6 bowls and used food coloring to make red, orange, yellow, green, blue and purple. My kids were really upset that indigo was absent. They know their Roy G. Biv! I cooked the layers in 8 inch pans. Luckily, I have 2, so there were only 3 cooking episodes - and because the the cakes were so thin, they only cooked for about 10 minutes each!
I used cream cheese frosting to fill and frost the cake. That's it! It was pretty quick and the wow factor is high! I chilled mine overnight and then let it come to room temperature before serving.