Preheat oven to 350º F (180º C). Grease both the bottom and sides of 3 (9-inch) round pans. Cut 3 (9-inch) circles out of parchment paper and cover bottom of each pan. Set aside.
In a large bowl, combine the cake mix, milk, yogurt, oil, and eggs. Beat on low speed for 30 seconds and then on medium for 2 minutes, scraping bowl occasionally.
Divide batter into 6 small bowls (about 1-1/2 cups into each small bowl). Mix 1 tablespoon of lemonade powder and 1 teaspoon of lemon extract into one of these divided batter batches and add a bit of pink icing gel until obtaining a bright pink. Set aside.
Pour 1/2 teaspoon of pure vanilla extract into each of the other 5 small bowls and stir to combine. Mix in the following icing gel colors to color each batter individually: Bright blue, yellow, violet, orange, and green.
See photo of the gel food coloring colors that we used.
Using an ice cream scooper or small cups, divide each of the six colored batters into the 3 prepared baking pans, first pouring one color into the center of the pan, and then sequentially pouring the next color into the center of the pan on top of the first, and so on, in a concentric bullseye pattern. Bake for about 36 - 42 minutes or until a toothpick inserted in the center comes out clean. Cover each pan loosely with a sheet of aluminum foil after half of the baking time has elapsed, in order to avoid browning of the top of the cake layer.
Remove pans from the oven and place on a rack to cool completely. Remove each of the 3 cake layers carefully from their pans, as well as from the parchment paper on the bottom. Assemble the layers of the rainbow butterfly cake, frosting between each layer with the buttercream and then frosting the top and sides of the cake (For the second layer of frosting, spread the frosting in swirls to make a cloud effect). Decorate as desired, and serve with a scoop of ice cream.