This cake was actually REALLY easy! I bought one box of white cake mix. ALL of the rainbow colors in food coloring gel.
Once I mixed the cake (following the box directions), separated the batter into 6 bowls and added the food coloring to make the colored batter.
All I did, seriously, was pour half of the batter from each bowl into the middle of the cake pan. And then again to the other cake pan. It turned out very pretty just sitting in the pan! Somehow the colors mixed like this.
I put both pans into the oven and baked it. I never understood evenly baking until I baked both cakes. I suggest you bake one cake pan at a time. It still came out alright but I wasted a lot of cake because of how unevenly it cooked.
We celebrated Hannah's 5th birthday last month....and collectively decided on a theme together. She had already had a princess theme for her 4th birthday and I wanted to encourage her to have something other than princesses. So, we agreed on a Rainbow Party!! It was fun for both of us. The only thing that she requested was to have a rainbow on top of the cake. I used mostly Skittles and some Jelly Beans. Did you know Skittles doesn't have blue in their candy assortment!?