So you've already had the rainbow grilled cheese sandwich for breakfast. What's for lunch? I suggest the rainbow pizza. Amy of the marvelous food blog Oh, Bite It made this pepperoni pizza with an extra thick layer of mozzarella on top.
As soon as she pulled it out of the oven, she dripped food coloring into the cheese and spread the colors through the cheese with a fork. It's like a food version of a sonic rainboom!