Preheat oven to 350°F. Line a 13"x18" half sheet pan with parchment paper. Set aside.
Prepare cake mixes according to package instructions. I included the ingredients that I added to my cake mixes which were 6 eggs, 1 cup oil and 2 cups water.
Divide batter equally into 5 bowls. Color each bowl of batter with food coloring of your choice. I used pink, orange, yellow, green and blue. Pour each bowl of batter into a large pastry bag.
Cut the tips off of each pastry bag and pipe batter onto prepared pan in straight lines going up and down (line will be 13 inches long) in alternating colors. Once you've piped all of the batter onto the pan, take a toothpick, insert into the middle of the batter and drag it to the outer edge, then back to the middle. Create a pattern as if you were drawing the spokes of a bicycle tire. This will create a tie dye pattern effect.
Bake cake for 25 minutes. Let cool. Refrigerate for 2 hours. Then cut 3 round 6-inch cakes using a cake cutter. Place first layer on cake plate, pipe dollops of frosting to cover the layer. Repeat with remaing two layers. Do not frost the sides. The cake is ready to serve.