Here's How To Enable OS X Yosemite Dark Mode
OS X Yosemite is the biggest visual overhaul Apple’s made to the Mac in years, but developers at WWDC seemed most excited about one tiny UI tweak – dark mode.Beta testers eager to try out the the new OS X 10.10 feature were disappointed to find out it didn’t make it into the first Yosemite beta, but our friend Jean-David Gadina, a developer at DigiDNA, has done some digging into the OS X Yosemite beta and discovered a new file not present in Mavericks that can be manipulated to enable the hidden dark mode feature.
How to enable OS X Yosemite’s dark mode.
Open your /System/Library folder by clicking Go >> Computer on the Apple menu bar, click your Yosemite drive then go to System >> Library
Open the CoreServices folder
Select System Appearance Bundle (left click)