Preheat the oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.

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

Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.

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

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

Divide the batter into three bowls and color each with blue, green, and purple food coloring.

Pour the colored batters into the prepared pans, alternating colors to create a marbled effect.

Bake for 25-30 minutes or until a toothpick inserted in the center comes out clean. Let cool in pans for 10 minutes before transferring to a cooling rack.

In a mixing bowl, beat the softened butter until creamy. Gradually add the powdered sugar and beat until smooth.

Add the heavy cream and vanilla extract, and mix until fluffy.

Once the cakes are completely cooled, place one layer on a serving plate and spread a layer of frosting on top.

Place the second layer on top and frost the top and sides of the cake.

Decorate with edible glitter and any additional decorations as desired.