How to remove BackgroundColor?

I don’t know how to remove a background color from my application window once it has been set.

In the IDE, I have set Has Background Color to disabled. In the code, the user can choose between a handful of colors. But it should be able to remove the background color, so that the operating system’s color appears again.

I tried Me.HasBackgroundColor = False, but that does not do anything. And setting an RGBA value (RGB with alpha/transparency) is not possible. So, what could I do? Any ideas? Thanks in advance.

My OS is Xubuntu 21.10.