Preheat oven to 350 degrees F.

Spray a 9 x 13-inch pan with cooking spray (even if it's a non-stick pan).

In a large bowl or stand mix fitted with a whisk attachment, mix together the cake mix, flour, sugar, and salt. Add in the milk, oil, extract, sour cream, and egg whites and beat for two minutes.

Add 1 1/2 cups of batter to one bowl and 1 1/2 cups of batter to another bowl, add red food coloring or gel paste to one bowl and blue to the other and stir until combined. Add as much as needed to reach desired color.

Pour the remaining white batter into the prepared cake pan. Pour the colors, one at a time, over the white cake by zigzagging across the cake. Use a knife to run up and down the zigzags to marble the cake.

bake for 25 to 25 minutes until cake comes clean when a knife or toothpick is inserted into the center. Allow to cool in pan completely before frosting.

Whip frosting ingredients in a large bowl or stand mixer with a whisk attachment. A stand mixer with result in a fluffier frosting, but frosting made with a hand mixer will do just fine as well and should give you enough to over the top of the cake. Whip for 2 to 3 minutes until light and fluffy.

Pipe frosting onto the top of the cake and sprinkle with red, white, and blue sprinkles.