How to decorate young male teen's room?

My 13 year old son loves outer space. So much so that my mom made him a denim quilt for his bed with the space shuttle on it. Over the past few years we’ve collected other “outer space” themed items. Problem is what color to paint his walls. I’ve got some wall stickers of planets so I was thinking a very dark blue and may be some glow in the dark paint for stars. But what about the other 3 walls? Help…