In DF it's possible to set the background image for the Windows Logon screen. The logon screen for Windows 8 also support changing the color (see http://www.eightforums.com/tutorials/40669-lock-screen-default-background-image-change-windows-8-a.html), but changing the background color in the settings doesn't change the color on the logon screen. Those two colors probably aren't linked together, but it would be a nice addition.