Preheat oven to 325°F and grease a 9x13 inch pan with cooking spray; set aside.
In the bowl of a stand mixer, add the cake mix, flour and sugar and mix.
Add the sour cream, butter, milk, eggs, and the almond or vanilla extract. Beat for 1 minute, scraping the sides down half-way through.
Decide how many different colors you'd like in the cake and divide the batter into bowls (one for each color). I chose four - yellow, pink, blue and green.
Add coloring to each of the bowls and mix until the color is evenly distributed.
Spoon the batter into the prepared pan, alternating colors, then take a toothpick and swirl the batter as much or as little as you'd like. (I don't recommend going too overboard with the swirling as it'll cause the colors to mix too much and could turn.....brown) :)
Bake for 30-35 minutes or until a toothpick poked into the center of the cake comes out with a few moist crumbs or clean; let cool completely.
To make the buttercream, place the butter in the bowl of a stand mixer and beat until smooth. Add powdered sugar, vanilla and 1 tablespoon heavy cream (or milk) and mix slowly until combined. Add additional cream as needed, mixing well between each addition.
Spread the frosting on as-is or add food coloring to create whatever look you're going for!