Mix white cake mix, egg whites, oil, water and sour cream for 3-4 minutes on medium speed. Split cake batter into three equal amounts, adding red and blue food coloring to two of the portions. Coat three, 4 x 9-inch bread pans with cooking spray and lightly flour the bottoms. Add the three batters to the pans and bake at 350 degrees for 18-23 minutes. Allow them to cool and remove from pans.