You can color and flavor royal icing with jell-o! If you want to add flavor but don't like the extra sugar, use unsweetened drink mix (Kool Aid). The flavor infuses the frosting and swirling it in can give a marbled effect. Use this in plain white cake mix also....same results!
Best of Recipe: RASPBERRY VANILLA JELLO SALAD. Could also use strawberry yogurt and add strawberries (and bananas if you like) instead of raspberries. Endless possibilities of yogurt flavors and fruit choices.