How to color the background of the margins in LibreOffice Writer?

See whether you can find such an option in LibreOffice's Format -> Page Style, or in the operating system's Appearance options.

However, the color of areas outside margins is unimportant, unless you have a bleeding printer.

> See whether you can find such an option in LibreOffice's Format -> Page Style, or in the operating system's Appearance options.

That's where I was looking, and I couldn't find it :/

> However, the color of areas outside margins is unimportant, unless you have a bleeding printer.

Indeed, but that's not the area I am talking about. I am talking about the actual margins themselves :)