I've got a split pane that contains a tab group pane, which in turn holds two content panes. I've set the background to be a custom colour - I initially set it on the tab group pane and set the content panes to have transparent backgrounds. This worked fine while the panes are pinned, but when the become unpinned, the background is always grey when you select one of the panes.
Is this to do with a trigger somewhere in the theme that always sets the background colour for an unpinned but visible pane?
When the ContentPane is unpinned, it is no longer contained within that TabGroupPane that contained it when it was docked. In this case the background is coming from the containing element - the UnpinnedTabFlyout. So you can either put a custom style for this element or to just control this brush, you can provide a custom brush resource keyed by DockManagerBrushKeys.UnpinnedTabFlyoutSplitterLightStrokeFillKey. e.g.
Thanks Andrew, that did the job perfectly!