I made my little ones a rainbow cake for a celebratory back to school dinner. They were thrilled! I started off with a plain yellow cake...
Then I divided it up into equal portions and tinted each bowl with gel coloring--it is more concentrated than regular food coloring. I bought mine in the cake decorating section at Michael's. I think it usually is used to tint icing.
Then I started adding the colors to my round cake pans. Here is where I realized I should have doubled my cake recipe...there really wasn't quite enough of each color.
Then I baked, frosted, and sprinkled with random Mickey Mouse sprinkles that I had in my cupboard. My little ones were thrilled to have cake on a non-birthday day...and even more thrilled to realize it was rainbow colors!!
See, it would have been even better if my layers were thicker...I'll have to remember that for next school year! This thread was my inspiration--lots of rainbow cakes to be found!