Ice cake. Using Black icing color, tint 1 cup icing black. Prepare two decorating bags with tip 45. Fill separately with black and white icing. Using ruler, find center of cake. Icing one side at a time, pipe vertical line of white icing along middle of cake. Pipe black line on either side of white line. With angled spatula, carefully smooth each line, one color at a time, wiping the blade after each pass to prevent streaks. Continue around each side and on top of cake, smoothing each line individually to prevent streaking. Chill cake until icing has completely set, about one hour.