In the Office2013 theme for both SIlverlight and WPF in the latest version, the RadTabItemStyle has the Office Black for unfocussed tabs. To fix this I added the lines: <Setter Property="Background" Value="{x:Null}" /> <Setter Property="BorderBrush" Value="{x:Null}" /> Not sure if that is the right place to fix it, because in the previous version of the Office2013 theme (where the RadTabItem had the right style) those 2 lines were not present. ========================== DECLINED DUE TO INACTIVITY.