AIs there a marshmallow frosting recipe that can be used to decorate a cake? I'll be covering the cake in frosting (no fondant), and decorating all over with multiple colors of frosting...will marshmallow frosting work or will it melt and slide off? Has anyone tried this?

You can color the marshmallow frosting, but you will want to use it the day you are serving the cake. It doesn't last longer than a couple days. That being said - you can't really decorate with it.