I like having a light green background i Writer because it is easier on my eyes, but I don't want that background to print. How do I create a non-printing background that will be set as te default page style?

This is a technical question about how to create non-printing page backgrounds in Writer.

Look once in the menu Tools>Options>LibreOffice Writer>Print. Do you have a check mark on “page background”?

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With me Windows 10 Home; Version 1809; 64-Bit | LibreOffice, Version: 6.2.4.2 (x64)…

Under Tools → Options → LibreOffice → Application Colors you’ll find the settings of all colors that apply to the program, not to the document: change “document background” to any color you want, that color will not go to print nor to PDF export.