Preheat oven to 350°F (175°C).
Mix dry ingredients in one bowl.
In another bowl, cream butter, sugar, and vanilla.
Add eggs, then alternate adding dry ingredients and buttermilk while mixing.
Stir in purple food coloring gradually to get the desired shade.
Divide batter into two 9-inch cake pans, filling each 2/3 full.
Bake for 25-30 minutes, rotating halfway through.
Let cakes cool in pans for 10 minutes before transferring to a wire rack.
For frosting, mix cream cheese and butter until smooth.
Add confectioners’ sugar gradually and beat until creamy.
Frost the cake, layering each tier with frosting and covering the exterior.
Decorate as desired and serve at room temperature.