3 cups powdered sugar
3 tablespoons butter, melted
3 to 6 tablespoons milk
1/4 teaspoon vanilla extract
1 to 2 drops each of green, yellow, red, and blue liquid food coloring
Stir together powdered sugar and melted butter. Add milk to reach desired consistency for drizzling; stir in vanilla. Divide frosting into 3 batches, tinting 1 green, 1 yellow, and combining red and blue food coloring for purple frosting.