We made this rainbow sheet cake for Kalla's 7th birthday party (see previous post).
It was a collaborative effort. We used two white cake mixes.
Divided the batter into 6 bowls. Approximately 1 1/4 C batter into each.
Then we mixed in some intense gel food coloring.
I used a large cake pan from Walmart wedding/cake supply aisle. I started out spreading the red batter at the bottom. After the first layer I wasn't able to spread the other colored batter on top without mixing the colors. So I drizzled each color in the order of the rainbow. All in all it worked out and we had vibrant pieces of cake. :)