My https://wordsandbuttons.online/ uses default browser colors for anything other than interactive illustrations. For those, I just don't know how to make user choice work with the graphics they show since the graphics is always different from picture to picture, so I impose slightly tinted background as part of the palette.
I don't see your point.
My job for the last decade has been to facilitate accessibility.
Not only have I never heard of this control existing in native Chrome, I can't figure out how to do it. I'm doubtful, then, that we can consider this a remedy of any kind for accessibility issues.
My hunch is that you mean that there are extensions that provide this – which I definitely have issues classing as "browsers providing" much in the way of anything.
Closest thing I can find are custom user stylesheets – which were removed in 2014 (also not sure if "write some CSS" is an a11y solution, heh): https://codereview.chromium.org/66383005/
I do agree the the actual point that the default colors have nothing to do with user preference though.