OS X Yosemite's dark mode, which was demoed on stage at Apple's Worldwide Developers Conference, has yet to make it into the beta as an available setting. It is, however, possible to get a glimpse of dark mode with a Terminal command, as discovered by iOS developer Hamza Sood
The command enables an early version of dark mode, which is clearly not yet complete, likely explaining why it is not yet officially available in the beta. Users should, of course, use caution when deciding whether or not to try this feature for themselves. Dark mode can be undone
with a second Terminal command.
The second beta of OS X Yosemite was released to developers earlier today, bringing several new changes like the return of Photo Booth and a new look for Time Machine. The public release of the software will likely come in the fall, after several more beta iterations.
OS X Yosemite