red, orange, yellow, green, blue and purple gel food coloring
3 cup unsalted butter, softened
1/4 cup heavy (whipping) cream
4 teaspoon vanilla extract
1 teaspoon salt
1 bag (32 ounces each) confectioners' sugar
cooked, cooled cake layers
Directions
Preheat oven to 350°F.
Spray three 9-inch round cake pans with baking spray.
Blend cake mix, water, eggs, oil and vanilla in large bowl with an electric mixer at low speed until moistened.
Beat at medium speed for 2 minutes.
Divide batter evenly into 6 bowls, about 1 1/2 cups each.
Add 1/2 teaspoon red gel to one bowl, 1/4 teaspoon yellow to another and 1/4 teaspoon orange to a third bowl of batter.
Stir each until blended.
Pour each into separate pans.
Bake 14 to 16 minutes, until toothpick comes out clean.
Cool 10 minutes.
Remove from pans to cooling racks and cool completely.
Meanwhile, add 1/2 teaspoon blue gel to one of the remaining bowls of batter, 1/2 teaspoon green gel to another and 1/2 teaspoon purple gel to the final bowl.
Stir until blended.
Refrigerate until ready to bake.
Wash, dry and spray cake pans with baking spray.
Pour each remaining color into separate pans and bake 14 to 16 minutes, until toothpick comes out clean.
Cool 10 minutes.
Remove from pans to cooling racks and cool completely.
Beat butter, heavy cream, vanilla and salt in large bowl with an electric mixer on low speed until blended, about 1 minute.
Slowly beat in powdered sugar until smooth.
Increase speed to medium and beat until light and fluffy, about 3 to 5 minutes.
Place purple cake layer on cardboard round.
Spread with about 1/2 cup frosting.
Top with blue cake layer and press lightly to adhere.
Repeat with green, yellow, orange and red cake layers.
Spread a light coating of frosting all over sides of cake.