 There is a "dark mode" in System Preferences which makes the Dock and menu bar darker.Apple initiated a new public beta program for OS X, a practice not seen with its operating systems since 2000's Mac OS X Public Beta, which had preceded the release of Mac OS X v10.0.Yosemite is part of the OS X Beta Seed Program, a public program that allows the first 1 million users to download and test the Yosemite beta at no charge.