I had tried this before, but just to be sure did it again now and restarted the MC and still nothing. I thought this setting (override w background was for the panel background?
It is very strange.. It works for me when I tries it.
(I was wrong about the "Override standard windows background" it does not need to be enabled.)
I enable "Use file specified background color", Then edit the color for focus and uncheck "Use default background color" and change the background.. Then OK.
then apply on the setting panel.
And now the color is changed.
Maybe it fails to save the config (Maybe you do not have permissions)
Press Ctrl+L and look at the bottom of the application log see if there is an error about not able to save. (It should show a dialog about that also , but maybe not )
Can you change other settings/color in the settings panel ?