Rainbow cake , AWESOME! description from baker: I just used box white cake mixes - 10 of them that I bought on sale. I had 6 6x6 cake pans and I mixed and baked 2 cake mixes at a time, divided them into 6 bowls and mixed in Wilton gel food coloring bought at JoAnns. It's not that hard to do. The hardest part was actually mixing all the icing up (it was a cream cheese frosting) - I had to do it in 4 batches because it just wouldn't all fit in my KitchenAid (powdered sugar everywhere).
5 ways to make cake mix better! Use double butter rather than oil, add an extra egg, use water instead of milk!