Windows 7 currently allows users to customize the Aero theme to a variety of colors and levels of transparency. Starting with Windows 8, this feature can now be automated by the OS to find a quick match between an ideal Aero theme color and the desktop background.
As reported by Within Windows, the new ‘Automatic’ option is available in the Window Color and Appearance settings under Personalization. As a user switches through various wallpapers, the Aero theme will change colors to match the background. Furthermore, it stands to assume that the feature would automatically operate if the auto-rotating desktop wallpaper timer was enabled providing users with a constantly changing Aero theme. The Desktop Background interface under Personalization also now features the option to allow the desktop wallpaper to be used for the logon and lock screens.
The screenshot below comes via Within Windows where you can view additional screenshots of the the Auto-Colorization feature.
Further reading: Aero, Windows 8