There is a gray area . . .
The advantage of all black, gray and white is that you can add just one color to it and give it some punch. So if he has a favorite NASCAR driver or sports team, pick their color and add a throw pillow or two, window valance and wall hanging.
As for the furniture, it's black or black. But you do have a choice between wood or metal. Either will look great. The wood absorbs more sound than metal and also gives a softer more traditional look. But if contemporary is his thing metal or clean lined wood furniture works.
Sauder has a really nice set in black that has several matching pieces that would work great in here. Oh and a little word of caution. Espresso brown is more popular right now than black, and brown is not black, so don't use it if he's wanting an all black room.
All he'll need is a bed, a desk for the computer and a dresser. That's what he thinks anyway. You'll probably want to add a nightstand, a few lamps and some storage pieces.
Neon goes over well in a teen boys gamers bedroom, as do black lights. So those would be welcome accent pieces. Pick up some posters of his favorite NASCAR drivers or sports teams, or even his favorite games and put on the wall, with black frames of course.
Check out Target.com for Teen Boys Gamers Bedroom Decor, as well as , RoomForKids Kid's Furniture. They both have a pretty decent collection for teens.
Speaking of Walls. . .
He'll probably want black walls too, and I leave that up to you. But my recommendation is to paint the wall across from the window white, and paint the remaining walls gray. If he insists, paint three walls gray and one wall black. The wall directly behind where he'll be sitting to play on the computer is the one to paint black. That'll help eliminate any glare on the monitor.
Windows . . .
Buy or make a roman shade for the window. You'll be hard pressed to find one in black. They aren't that difficult to make if you really want to put a black one in there. Check out DIY Decor for some sources for how to make them. If you don't want to mess with that, a black miniblind works just fine. (That's what my son got.)