LEGO has released a black NXT brick that is identical to the original white NXT brick. The only things that are different are the plastic color and the price.
Note that this is only the programmable brick, not the full retail kit. This brick is intended for LEGO enthusiasts that already have the full NXT kit and want something unique.
If you are buying another NXT brick, which you’d need if you want to run two programs at once, the black brick is currently $170, while the white brick is currently $145. The full retail kit (white) is $280.