While the only visible difference between the black Motorola Q, and the $50 cheaper regular Motorola Q is the coat of paint, there are actually various improvements on the inside as well.
There's improved power management that gives you longer battery life, Bluetooth headset volume control, email client fixes, and a rubberized grip for less slippage. Seeing as it's only $50, and the black does look better than the silver, we'd recommend this improved one over the original. But you knew we would say that.
Black Q: It's What's Inside That Counts [Crunchgear]