Put scrapbook paper on it. My dd gave me this idea for my craft room. I love it is't very colorful.
Another one of her ideas hang interesting fabric. I think of it sort of like hanging a tapestry. I have also hung quilts.
Cover it with pictures, posters, different objects. I didn't do it here but I like to mix pictures with dimentional objects like I did with my bird pictures in the library here.