Keep it light
One way to use black in a bathroom without overwhelming the space is to use black in details and contrasting elements, and not as a main color. You can have black in smaller touches and yet keep its wonderfully elegant look. The trick here is to balance the amount of black and white more or less equally. The wallpaper does this by itself, but note how the bottom half of the wall balances the dark tile of the floor. Minimal pedestal sink, simple mirror with a black frame, and a simple hanging light with a black shade. A touch of brass finishes the look for some brightness and color.