Make layered cake. Prepare batter following recipe directions. Bake and cool two 6 in. cake layers. Prepare buttercream icing following recipe directions. Level, fill and stack layers on cake circle for a 2-layer cake, 4 in. high.

Ice cake. Use spatula and white icing to ice cake smooth.

Mark cake. Place right angle of ruler 3 inches from edge of cake. Use toothpick to trace triangle in icing. Flip ruler over, moving downward on an angle for side of cake, making sure to match triangle from top of cake. Use toothpick to trace this triangle in icing.

Decorate cake. Use blue decorator icing pouch with coupler and tip 10 to outline triangles on top and side of cake. Use white decorator icing pouch with coupler and tip 10 to outline two rows inside blue diamond. Use black decorator icing pouch with coupler and tip 10 to outline and fill in center of white diamond.

Use white, yellow, black and blue decorator icing pouches with couplers and tip 10 to outline additional diamonds outside of blue one following this pattern: two white, one yellow, one white, one black, two white and one blue. Continue piping this pattern until cake is covered.