The build is unstable according to Kaseb, but if accurate, it shows an interesting design direction for Google+ as an app, and it could also point to design ideas that Google has in mind for the entire Google user environment as a whole.
The action bar at the top is color matched with the button to post an update. This design language is consistent with the leaked Gmail and Google Calendar images we saw earlier this month. The overall appearance is “flatter” but layered. Certain items float above the screen, but are comprised of the new flat motif that is in style right now.
To his credit, Yoel is verified on Google+, and the design cues are not outrageous, so while we cannot 100% confirm these images are real, we are comfortable with the source given the previous news we have seen over the past couple of weeks. Based on that, Google+ has a reddish-orange color scheme, Gmail looks blue, and Google Calendar is lavender. Maybe these colors will be user customizable.
sources: +Yoel Kaseb (Google+) via Android Police