Using the Ribbon, I can set the background property to Black. This doesn't set the entire background to black, but only appears to set part of a gradient to black, leaving the top half of the tab's panel with a gradient fade to white. (or maybe it's a clear
to white gradient overlaying the black background).
I'd provide an image but I can't find any tools allowing me to upload one. The XAML to reproduce is quite simple however, just start a new project with a the Ribbon for WPF (downloaded from
http://www.microsoft.com/downloads/en/details.aspx?FamilyID=2bfc3187-74aa-4154-a670-76ef8bc2a0b4) and set the Ribbon's background to black: