Preheat oven to 350°F. Grease and flour three 9-inch round cake pans and line with parchment circles.
Cream butter and sugar together until light and fluffy.
Add eggs one at a time, mixing well after each addition. Stir in vanilla extract.
Whisk flour, baking powder, baking soda, and salt in a separate bowl.
Add dry ingredients and buttermilk alternately to the butter mixture. Mix just until smooth.
Divide batter evenly into three bowls. Tint one pink, one yellow, and one blue using gel food coloring.
Pour each color into prepared pans.
Bake for 20 to 25 minutes, or until a toothpick inserted in the center comes out clean.
Cool in pans for 10 minutes, then transfer to wire racks to cool completely.
Beat butter for frosting until creamy.
Gradually add powdered sugar, mixing well.
Add vanilla, salt, and heavy cream. Beat until smooth and fluffy.
Place blue cake layer on serving plate. Spread frosting evenly on top.
Add yellow layer and frost. Place pink layer on top.
Apply a thin crumb coat around cake and chill briefly.
Frost entire cake smoothly.
Press Bunny Peeps around edges of cake.
Fill center with green coconut flakes and decorate with Easter M&M’s candies.