Center two racks in the oven and preheat the oven to 350°F. This ensures an even bake.
Spray three 8 or 9 inch round cake pans with nonstick spray. Add a spoonful of flour to each pan, shake it around, and tap out the excess. This prevents sticking.
Sift together the cake flour, baking powder, and salt in a medium bowl. Sifting aerates the flour, giving the cake a light texture.
In another bowl, whisk together the buttermilk and egg whites until well combined. This mixture adds moisture and lightness.
In a large bowl, use an electric mixer to blend together the butter and sugar. Beat at medium speed for a full 3 minutes until the mixture is very light and creamy.
Add in the vanilla extract, then gradually mix in one third of the dry flour mixture while still mixing on medium speed.
Next, add half of the buttermilk and egg whites mixture and continue mixing. Follow this with half of the remaining dry ingredients until fully incorporated.
Add the rest of the buttermilk and egg whites, then finish adding the last of the dry ingredients. Mix well for a full 2 minutes to aerate the batter.
Divide the batter evenly into three separate bowls. Color two of the bowls with gel paste, one dark red and one dark blue. Adjust the color until you achieve your desired hues.
Scoop each colored batter into its own prepared cake pan. Use a spatula to smooth the tops for even baking.
Bake for 20 to 25 minutes for the 8 inch rounds (or 15 to 20 minutes for the 9 inch pans), or until the cakes have risen and spring back when touched. A toothpick inserted into the centers should come out clean.
Transfer the cakes to a cooling rack and cool for about 5 minutes. Run a knife around the sides to loosen them, then invert the cakes and cool to room temperature right side up on wire racks.
Once cooled, frost the cake as you would a three-layer cake, applying frosting between each layer before covering the entire cake.
