Thumbnail background color: How to set?

[ubacher]

In Preferences -> Application -> User Interface -> Thumbnail background color one can set the color.
I find, however, that that does not work.

Now there is another setting in the thumbnail layout editor: Panel Background.
There are two (applicable) settings: 1. File Windows settings, and 2. No.
Flipping between those two settings causes a change in darkness but nothing else.
(The description for both of these settings is the same!)

Background: I find that on my laptop, on certain surrounding light, it is difficult to see the difference between a selected file (wine color) and
an unselected file (dark gray color). So I was actually looking for the setting for the thumbnail background when selected. There is now such setting I
could find. That's when I started looking at the default thumbnail background color and found I could not change it.)

Bug or lack of understanding?

[Mario]

I can't follow, sorry.

You can fill a thumbnail with a color. This color is applied when the thumbnail (image) is not quadratic (to fill the left/right top/bottom margin). By default this is off and the background color set for the panel is used. The colors of the panel control how selected, focused and normal files look, e.g. "background color (selected)".

[ubacher]

The colors of the panel control how selected, focused and normal files look, e.g. "background color (selected)".

What setting are we talking about here? Preferences -> Applications -> Colors?

When I change the Dark Background Color from black to pink it does not change the background of the thumbnail panel.
See screenshot.

What about the setting Thumbnail background color?

[Mario]

File Window Settings.