Confusing behavior with "Master Background" checkbox in sidebar in "Properties"

[EmilySeville7cfg]

I have a colored master slide with a pink background and a derived slide from it. When I choose custom color on my slide and uncheck Master Background checkbox I obtain no background color at all. It’s an unexpected behavior (from my perspective). But when I check it my custom background is applied to slide. Why it works as it works? Why custom background appliance requires Master Background checkbox.

I post my question here because my original one didn’t get any response.

[Hrbrgr]

After you have given your master slide a background color, check the box for “Master background”.
If you now create several new slides on this basis with Ctrl+M, all slides are initially the same.
But with the checkmark Master background you can determine individually for each slide whether the background should be displayed or not.
This way you have a master slide, but you can still treat the presentation slides differently.