I have a request for a batman cake with the black icing but she wants peanut butter icing, is there a way to do that without covering with fondant? I don't know how you would make that black. She also wants a superman cake with creamcheese icing which would be red. Not aware of a way of doing that either without fondant.
I think the best way would be to cover them in fondant. The peanut butter I have seen a recipe for peanut butter ganache that also has dark chocolate so would make it a darker brown and you could add some black food coloring. Not sure if that would work. With the red, if you do decide to use fondant, be careful with cream cheese icing under fondant. Some recipes do not work well under fondant.