In none of our themes is the background of the PaneHeaderPresenter Transparent by default nor do they react to the mouse being over them. Since you mention a TabGroupPane perhaps you mean the tab item? If so then you can look at the DefaultStyles and locate the Style for the PaneTabItem to see where the Background is coming from. In the case of dockable tabs (i.e. not unpinned and not in the documentcontenthost), the background depends on the TabStripPlacement (which in this case defaults to the bottom). In that case the default background comes from a dynamic resource to a key of "{x:Static igDock:DockManagerBrushKeys.TabbedListNotActiveBottomCenterFillKey}". So you could put a Brush with a key of this value into the app's resources and that should affect the background of these tab items docked and floating. Note if you are setting the Theme property then you'll have to put this brush into the XamDockManager's Resources (to affect the docked tabs) and also need to hook the ToolWindowLoaded and put this into the e.Window's Resources if you want to affect the floating tab items.