Google+ social sharing button designs have been updated and automatically rolled out to websites. The rollout was fairly quiet. There were no big announcements or press releases from what we can tell, other than a post in the Developing with Google+ community on Google+. Fairly smart of them to release the news exclusively on their own platform.
The new buttons do away with the grey background, and now are cleaner and (as a result) have sharper contrast and readability.
Above: The newly designed Google+ social sharing buttons: in all sizes and formats.