Facebook has yet to make an official or formal announcement where this brand new user interface is concerned, which will see it introduce a more consistent and colorful iconography to the menu panel, in addition to a flattering look on the whole. Of course, it remains to be seen whether the major effort will be taking the Material Design route, or Facebook could just be making use of some Material Design guidelines which was Google had put out earlier in the year.
It does seem as though this is only for Android, and the distribution pattern happens to be fairly random. Hopefully something official will be revealed soon. After all, it is not as though Facebook had been shy of experiencing its fair share of new updates and changes along the way, right?