Meanwhile, using long serrated knife, trim 1/4 inch off short sides of cake and 1 inch off long sides of cake. If necessary, cut rounded top off cake to make a level surface. Cut cake lengthwise into two pieces, one about 8x6 inches and one 4x6 inches. Place pieces, cut side down, on individual plates. To seal crumbs, frost top and sides of 8x6-inch cake with thin layer of red frosting and the 4x6-inch cake with thin layer of yellow frosting. Freeze pieces 30 minutes to set frosting.