Tone-on-tone cakes are simple but super artistic. You can use the same color icing that's on your cake to create a decorative texture element, such as a snowflake, scrollwork, flowers, fleurs de lis, letters, or any other elements you love.
Divide your regular Costco sheet cake into sections, and slice them down the line. For each mini-cake, smooth over any messed up icing. Using the piped icing you can buy in stores, draw out snowflakes, flowers, letters, stars, or any other decorative element across the top and sides. Finish it off with a few dustings of edible glitter or luster dust, and you have a group of elegant cakes with different design motifs. Don't need to use them all right now? You can freeze undecorated portions with the icing smoothed out and decorate them at a later date.