Preheat your oven to 350°F (175°C). Grease and flour two round cake pans to prevent sticking.
Cream together the softened butter and granulated sugar until light and fluffy, about 3-5 minutes.
Beat in the eggs one at a time, ensuring each is fully incorporated.
Stir in the buttermilk and vanilla extract until well combined.
Whisk together the flour, cocoa powder, baking powder, baking soda, and salt in a separate bowl.
Gradually add the dry ingredients to the wet mixture, mixing until just combined. A few small lumps are okay.
Divide the batter into different bowls, adding purple food coloring to one and mixing until you achieve your desired shade. Repeat with additional colors if desired.
Carefully divide the batter evenly between the prepared pans and smooth the tops with a spatula.
Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
Cool the cakes for about 10 minutes in the pans before transferring them to a wire rack to cool completely.
Frost with buttercream frosting and decorate with edible designs.
Notes
Ensure ingredients are at room temperature for better mixing. Avoid overbaking to prevent dry cake.