My daughter requested a rainbow cupcake for her birthday...with cake ball toppers. I decided to make rainbow cupcake toppers to go on top of rainbow cupcakes, pillowed with marshmallow frosting.
First, you have to make your cupcake toppers. You need a candy mold (one that looks like Reese's) from the craft store. You will also need candy melts in rainbow colors, or you can make your own colors using candy color and white melts. Start with your cake ball mixture. Add some melted candy to the mold, place a small amount of cake ball on top, and cover with chocolate. It doesn't matter what the top of the mold looks like; you're going to cover it with frosting. Freeze to harden the candy, pop out the toppers and repeat with remaining colors.
Then, you need to make your rainbow cupcakes. You need to use a box of white cake mix, divide it amongst six bowls and color with food coloring. Layer the cupcakes, starting with purple at the bottom, then blue, green, yellow, orange, and, finally, red on the top. Bake and cool. Then frost with white frosting.
Top with a cupcake topper and frost the topper with white frosting as well. Viola - a cupcake topped cupcake... that's rainbow inside.