Preheat the oven to 350 degrees and spray the 3 cake pans with pam baking spray
Combine all cake ingredients into a standing mixer or large mixing bowl and beat until combined
Divide the batter between 5 medium bowls
Mix in a few drops of one color into 1 bowl and mix until combined
Repeat with remaining colors
Drop dollops of the colors into the three cake pans
Bake in the oven for 25-32 minutes or until a toothpick comes out clean
Allow to cool completely before moving onto the cake board
Using a cake leveler, remove the dome from the cakes to make even
Using a standing mixer, beat together the butter, powdered sugar, vanilla, and heavy whipping cream until combined, smooth and stiff with peaks
Scoop 1/2 C of frosting into 6 bowls
Mix in a few drops of a color into 1 bowl. Repeat steps for remaining colors