So, I've been seeing this "rainbow cake" around the blogosphere, and I decided I wanted to try and make it. So, I googled it and found a bunch of different sites on how to make it. None of them were very clear though, so I thought I would post how I made this cake.
First, I bought a regular white cake mix. After you make the batter, divide it into 6 equal parts (about 1/2 cup + a couple tbsp.) You can use food coloring to color the batter, but for brighter colors, I decided to use the Wilton gel. If you use food coloring, it will turn out more pastel. And yes, you have to dirty every dish in the house, but it's worth it!
This recipe works best if you have 2 round pans. Mine are 9". Make sure you pour each color right into the middle of the pan. It will spread out on its own. First, I poured in purple, blue and green. Then I did red, orange and yellow. Normally you would do yellow, orange, then red, but I turn my top half upside-down, does that make sense. Basically, when you have both halves of the cake on top of eachother, you want the color scheme to go in rainbow order.