Seperate yellow cake batter in 3 seperate bowls. In one bowl, add red coloring. In the other add blue and in the other add yellow. For additional colors mix in the little coloring bottle lid yellow and blue for green, and red and blue for purple. You now have 6 different bowls with different colored batter. Now, get a baking pan (one that you would use for yellow cake) and pour all four/six in different sections of the pan. Once you are done with that the pan will have all six/four colors seperated looking like a rainbow wheel :D.