Q: I'm a 15 yr old guy.
A: It may look great to paint your room a bright or very dark color, but you will probably get tired of it quickly. If you are like most 15 year old guys you probably have posters, sports stuff, etc. on your walls. Try painting it a more neutral color like beige, tan, light grey, etc. This will show off your stuff better. If you want you can paint one wall a different color as an accent wall. The one behind your bed would be great. For inspiration look at the colors of the things in your room and pick one of those. Good Luck