Preheat the oven to 350°F (175°C). Grease and flour three 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, combine the flour, baking powder, and salt. Gradually add to the creamed mixture alternately with milk, mixing until just combined.

Divide the batter into three bowls. Color one bowl red with food coloring, one blue, and leave one plain for the white layer.

Pour the red batter into one prepared pan, the white batter into another, and the blue batter into the last pan.

Bake for 25-30 minutes or until a toothpick inserted into 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 powdered sugar and mix until smooth. Add vanilla and milk, mixing until desired consistency is reached.

Once the cakes are completely cooled, place the red layer on a serving plate. Spread a layer of frosting on top.

Add the white layer on top of the red layer, then frost the top of the white layer.

Finally, place the blue layer on top and frost the entire cake with the remaining buttercream frosting.

Decorate the top with blueberries, sliced strawberries, and optional white chocolate stars.