Google is testing a new color for their top navigation bar. Since June 2011 Google’s top bar has had a black background color with white/gray text overlaid. Google is now testing changing the background color to a gray/white with black/dark gray text overlaid.
The picture above is from former Googler, Pedro Dias Google+ page.
It seems many searchers have begun seeing the new gray top bar as early as this past Saturday and more and more searchers are now seeing it.
I personally do not see it yet. It may be a test or it may be something Google is rolling out to their user base. I’ve sent an email to Google to find out.