If you head over to one of the five major carriers in the U.S. you can select the black or white variants in the store or select the Moto Maker option. The Moto Maker Option seemed to be limited for AT&T customers for now but will likely be available across other carriers in the near future.
Check out the Moto Maker in action in the following video demos:
Selecting the Moto Maker option will get you a redemtion card which can be redeemed online at motomaker.com or Motorola.com/designit. Here you can choose from 2 front colors, 18 back colors with the option of custom engraving, custom boot messages, 2 storage sizes, 7 accent colors, 16 unique wallpapers, the color of your charger and matching in-ear headphones.
Motorola will even offer a wood grain option to customize your handset in future.
Because the device is being assembled in the U.S. Motorola is able to have the device built and shipped to you for FREE in roughly four days. However this may be delayed if they don't have a particular color, pattern or accessory you need in stock.