I had an idea on how to get a rainbow cake with just four pans. If I colored two portions of cake batter for each pan I could have eight colors. I separated the batter evenly between eight bowls and colored each bowl with drops of gel color. Since the convention is to name seven of the rainbow colors, I made the eighth color pink (although it was tempting to make it greenish purple like octarine as a nod to Terry Pratchett). I put one color in each pan, then dolloped the second color on top before spreading it out to get a slightly marbled effect. The cake came out more like a spectrum! Hurray!