Mac likely did use this scheme, and yes, copied it from Xerox. However neither Macs nor Xerox had mainstream use. I'd only actually seen 3 Macs in the wild before their switch to Intel, over 20 years later.
Windows adopting the "paper"-white background and whole world drooling over the arrival of Windows 3.1 and 95 is when it became the standard, I think.
There's no 'likely' about it - the Mac absolutely used white as its background color for document windows and finder folders. It was striking and different when you first encountered one of the early compact Macs to see how white the screen was when you opened MacWrite.
As for the claim that Macs had no 'mainstream use' for 20 years until the Intel switch... your personal Mac-free life is a sad story, but not remotely universal, and while it's certainly true that Macs always had minority market share, it's insane to suggest they weren't influential.
My favorites were actually DOS TUIs, where for some reason blue became a commonly used background color for a lot of things (e.g. Norton Commander, many Borland products, FoxPro...).
Windows adopting the "paper"-white background and whole world drooling over the arrival of Windows 3.1 and 95 is when it became the standard, I think.