When you've finished a game with your friends, you'll now receive a new color or accessory as a reward!
This was supposed to be in the first release, but apparently it wasn't working. Whoops!
Source: Steam Community (opens in a new tab)
Build and release context
Steam update times within 24 hours of this post. Matching dates do not confirm which build it describes.
Build 12645043 · public branch
Steam updated · First observed