+1

On a dual-monitor setup I'm also getting this effect on the window without focus.

The following screengrab is not how it looks to the naked eye:
0_1547723850476_Screenshot 2019-01-17 at 11.08.59.png

When I opened the screengrab in an image editor the icon background is transparent with white icon.. actual appearance to the eye is black background white icon like this:
0_1547723888579_Screenshot 2019-01-17 at 11.08.59-edit.png

Thanks for the feature request @Tomáš-Rus - we haven't done this yet (would need to implement the pref pane as you say.