Preheat your oven to 350 degrees Fahrenheit. Grease and flour three 6-inch cake pans and set aside.

In a large mixing bowl, cream together the softened butter and sugar until light and fluffy.

Beat in the eggs, one at a time, making sure to fully incorporate each egg before adding the next.

Add in the vanilla extract and mix until combined.

In a separate bowl, whisk together the flour, baking powder, and salt.

Gradually add the dry ingredients to the wet mixture, alternating with the whole milk, and mix until just combined.

Divide the cake batter evenly between three bowls.

Using food coloring, tint one bowl of batter red, one blue, and one purple.

Pour the colored batters into the prepared cake pans, making sure to spread the batter evenly.

Bake the cakes for 20-25 minutes, or until a toothpick inserted in the center comes out clean.

Allow the cakes to cool completely before removing them from the pans.

While the cakes are cooling, prepare the frosting. In a large mixing bowl, cream together the softened butter, powdered sugar, and vanilla extract until light and fluffy.

Gradually add in the whole milk, one tablespoon at a time, until the frosting reaches your desired consistency.

Divide the frosting evenly between three bowls.

Using food coloring, tint one bowl of frosting red, one blue, and one purple.

Once the cakes have cooled, place the purple cake layer on a cake plate or serving dish.

Spread a thin layer of purple frosting over the top of the cake layer.

Place the blue cake layer on top of the purple frosting, and spread a thin layer of blue frosting over the top.

Finally, place the red cake layer on top of the blue frosting, and spread a thin layer of red frosting over the top.

Use the remaining frosting to cover the sides and top of the cake, creating a smooth and even layer.

To decorate the cake, use a toothpick to draw a line across the top of the frosting, creating a grid pattern.

Use additional frosting and food coloring to create colorful swirls and designs on top of the cake.