Prepare cake mix per directions on box, however, substitute water with any clear soda. (Sprite, 7-Up, Gingerale, etc.)

OR

Substitute all ingredients (water, oil, eggs) with one can of clear soda (Sprite, 7-Up, Gingerale)

Separate cake batter into 5 or 6 bowls (depending on the number of colors you want).

Each bowl should contain less cake batter than the one before it.

Add desired food coloring to each bowl of batter. Food coloring boxes have ratios to make special colors (i.e. purple, Orange, real, etc...)

Once you've colored your batter, pour the batter into your baking dish beginning with the bowl containing the most batter. Pour subsequent batters directly on top of one another forming a rainbow effect.

Bake cake as per directons on the box.