Dark Mode changes the appearance of the Dock and menu bar to a black color , style very different from white / silver interface system.
A developer / hacker on Twitter has discovered, interestingly, a way to activate the Dark Mode in Sierra macOS while testing the Beta version.
Dark Mode can be enabled in Safari and System Preferences
Guilherme, the developer who has discovered the tip, has not made clear which method or technique has been used to activate the Dark Mode in macOS Sierra, and has not indicated whether it will publicly unveil soon.
The functionality Dark Mode is one of the most requested by users of OS X and Mac OS Sierra, even in IOS 10. This is because many people do not like the appearance of the user interface, and others would like to have a special way to use the Mac (iPhone, or iPad) at night.
For now, it is quite unlikely that Apple implement the Dark Mode in iOS 10 or macOS Sierra, but perhaps in future versions functionality comes to both operating systems. For now, users of iPhone and iPad, we settle function Night Shift introduced in iOS 9.3.
macOS Sierra at # WWDC16