GTK 3: How to make items a different color when the application loses focus?

Question

I'm trying to edit a GTK3 theme to make it behave a little better, and I'm stuck on one issue: The color of active/selected items remains the same whether the application has focus or not. Can someone tell me what selectors distinguish an item in an active window from one in an inactive window?

Answer 1

Apparently, gtk3 supports an undocumented :backdrop selector that should do what I want under window managers that support the _NET_WM_STATE_FOCUSED extended hint. Sadly, it does not work on most window managers because most do not support that hint.

UPDATE: A patch is now available for Xfce's xfwm4 window manager.