Since 2015, it is possible that the Do You can also dip the menu bar into a dark design. The Finder, Safari, and other Apple applications were not affected by this change. With macOS Mojave the dream however was and Apple donates the Mac users a real Dark Mode, which system-wide to the employment comes. In order to use the dark appearance, a previous activation is required.
How to enable the Dark Mode on macOS Mojave
As with activating the dark dock and menu bar theme, first click on the Apple logo in the menu bar at the top of the screen. Now select the option "System Settings". Then click on the entry "General". At the top you can see the setting for the "appearance". Select "Dark" and your Mac will be dipped in dark colors. Clicking on "Bright" deactivates Dark Mode.
Note: Note that Dark Mode affects all Apple apps such as Safari, Finder, Mail, Calendar, Notes, and other apps. For third-party providers, it is not always the case that the app is dipped in dark colors. Here it depends on the integration of the feature by the developer. Popular apps will probably get the release of macOS Mojave or shortly afterwards a corresponding update.