Apple Seeds OS X 10.10 Preview 3
Following the seed of iOS 8 beta 3, Apple has now seeded the third preview of OS X Yosemite to developers. This version comes two weeks after the second seed. This version now includes a dedication option to enable the dark mode that Apple talked about at WWDC. Up until now there was no way to enable the dark mode that Apple talked about. There's also a few interface tweaks, including some changes to the System Preferences app.
Developers can update to preview 3 in the Mac App Store > Updates > Software Updates > OS X 10.10 Preview 3. If you don't have OS X Yosemite yet you can download it for the first time in the Mac Developer Center.