Allow us to set the Background Color for light and dark wallpapers

[LuukDomhof]

Describe the enhancement or feature you'd like
When setting a wallpaper, Windows allows users to set a background color too. This background color is used to fill any areas not filled by the wallpaper.

AutoDark can automatically adjust the wallpaper based on Light and Dark mode, but it lacks an option to change the Background color for each. This means the desktop can get mismatched colors when the user has a custom background color set.

Additional context
See images below for an example.

A mismatched desktop because the background color is set for light, but can not be updated by Auto Dark when switching to a dark background:

The setting in windows:

[ChenYiLins]

This is indeed an omission. In Fit and Center modes, you should be allowed to set the color of the uncovered area of wallpaper.