Our little one's belated birthday party this year was loosely themed "rainbow." Not so much as in a picture of a rainbow, but more so inspired by the bright colors. The fruit platter was arranged in color order. The goody bags were a set of rainbow colored bath crayons. And the cake, though plain on the outside, was filled with colorful, FANCY fun.
I made six 2" cakes - one of each color of the rainbow. When they were done baking I cut them in half (so I had 12 "cakes"). I layered one of each color with icing in between (x2 - we ended up with 2 full sized cakes) and covered it with white icing. No one knew of rainbow until we cut into the cake. It looked beautiful (more beautiful in person than this picture shows) and Layla LOVED it.