In June, Google began testing a black navigation bar that appears at the top of Google product pages, like Google Reader, Google+, Gmail, and Search. It replaces the old white bar, and gives you quick access to the company's services, including Google+ notifications and account settings.
If you're an avid Googler and miss the convenient navigation bar while browsing other sites, the +Everything Chrome extension might be your answer.
Once enabled, the black bar will appear at the top of any Web site, giving you access to Google services and your Google+ notfications. But if you want to hide the bar on any given Web site, click Hide in the middle.
Of course, if you find that you despise the new navigation bar, and wish to revert to the classic white theme, there's an extension for that, too.