Strange. My revisions are in green and when I’m done, I select all and change to black. some text doesn’t change color and stays in green. Weird eh?
I would try using the dedicated command to strip revision markings out, which you’ll find in the Format ▸ Revision Mode ▸ submenu. They are still working on cleaning up the implementation, which uses a special code in addition to setting text colour (or maybe even entirely the code and no actual text colour is involved, as I think earlier implementations did). In the future it should be purely text colour, so that using the “remove color” command would work.