Decorate cake. Use spatula and white icing to ice top of cake into a spiral design. Starting at the top edge of cake, use tip 18, cut disposable decorating bag and red icing to pipe two shells in opposite direction of each other. Continue piping shells down the side of the cake. Use tip 18 and blue icing to pipe two rows of shells. Use tip 18 and reserved white icing to pipe two rows of shells. Repeat until side of cake is covered.