If you download GLTron, you can easily change the backgrounds and trails. Here is how I did it.

Open the Art file, open the classic artpack, drag the files into an art program (photoshop) and change the way it looks. Save it in a different folder and keep the name of the files the same as the original. You have to save thefiles as .png, or they will not work. Once you are finished remodeling the files, name your folder what you want the game to be called. When you play GLTron, go to Video, and select your artpack. The music can be changed. Get an mp3 and put it in the music folder. There is something else you need to do, so check the read-me. It is really fun!