They love switching up the colors because to them it's a completely different frosting even if the flavor is the same.
One of our favorite recipes is this Creamy Vanilla Almond Frosting. I took a basic buttercream recipe and changed it up a bit. By adding some cream cheese, the frosting takes on a creamier consistency. You don't add enough to turn it into cream cheese frosting though. Then, to compensate for the cream cheese that has been added I add a bit of extra powdered sugar so it is still thick enough for piping and maintaining its shape. Add a little bit of almond extract and you've got a brand new frosting.
This recipe is great for cupcakes, of course. Vanilla-almond is a great flavor combo for white cake and chocolate. We like to fit the bag with a star tip (Wilton 32) and dot the tops of the cupcakes with lots of stars. Just squeeze and pull up for each star dot. I like to use disposable decorating bags for the frosting because it makes clean up fast and easy.
You can also use this frosting for cakes, but my kids usually don't have the patience that is involved for waiting for the cake to bake and cool before frosting it.