When my sister got married, she had a rainbow theme for her wedding. I decided to try to incorporate her theme into the cake I was making for her bridal shower. After a quick search online, I found a link to a fun and relatively easy tutorial at Omnomicon.com. I used my own cake recipe and then just followed the instructions for coloring the batter. The cake was a huge hit with the bride and all of the guests.
Essentially, you mix up your cake batter, then separate it into 6 small bowls. Add a different color to each bowl. Then drop the colors one at a time into the center of the pan and bake. Click on the image below for the more detailed tutorial from Omnomicon.
I decided to frost the cake with gray frosting to offset the colorful surprise inside.
Not only did the inside look fantastic, it tasted great too!