The Ultimate Rainbow Cake ─ Cake Style

Ingredients
7 1/2 cups cake batter, divided into six parts and colored red, orange, yellow, green, blue and purple using gel food colors
4 pounds, 15 ounces buttercream, colored as follows:
- 1 pound, 10 ounces plain
- 8.8 ounces red
- 8.8 ounces orange
- 8.8 ounces yellow
- 8.8 ounces green
- 8.8 ounces blue
- 8.8 ounces purple
6 cake pans, 9-inch
Spray oil or butter for coating the cake pans
Parchment paper
Spatulas
6 piping bags, 12-inch
1A piping tips
Turntable
10-inch round cake board
Scissors
Directions
1. Spray cake pans with nonstick spray or rub with butter, and then line using parchment paper.
2. Divide 7 1/2 cups cake batter into six small bowls. Add gel food colors and stir. Pour into cake pans and bake each cake at 340 degrees Fahrenheit for 18 to 20 minutes, or until a toothpick comes out clean.
3. Allow to cool in their pans for 10 minutes before turning out onto a wire rack. Allow to cool completely. Wrap in plastic wrap; chill one hour.
4. Stack the cake and apply plain buttercream to each layer, starting with purple on the bottom, then blue, green, yellow and red. Apply a crumb coat of buttercream to the sides and top of the cake. Chill in the fridge for 15 minutes.
5. Fill a piping bag with purple buttercream and apply dollops to the cake with a 1A tip, dragging as you go. Once you have gone all the way around the cake, pipe the blue buttercream in the same way. Continue up the cake in the same order of colors as the layers until the sides are done with all six colors.
6. Starting again with purple, repeat the process on the top of the cake, working your way into the center, and ending with the red buttercream.