Any aspect of the controller, from the buttons, to the sticks, can now be modified to look however you want. Heck, you can now engrave controllers with text of your choice.
Here's a trailer:
The Verge says these controllers cost $US79.99 ($108) each, with an additional $US9.99 ($14) for text. Every custom controller is actually the new redesigned pad, which will first launch with the release of Xbox One Slim. This means any custom controller will come equipped with a new textured grip, and increased wireless range, among other improvements.
It's all being done as a part of the "Xbox Design Lab" and Microsoft says you'll be able to use it via Xbox.com. (The site isn't live yet though.)
I gotta say: some potential controller configurations look oh-so-hot. I'm excited to spend way too long picking out colours whenever this officially launches.