A family of Microsoft word processing software products for creating web, email, and print documents.
I am also seeing the behavior using Word for Mac, v15.32.
It does seem like when I open the document and pick up editing from where I left off, the color changes, however my user name on the right is identical. I tried saving and going back into the document and the color goes back to the original color, however new changes entered after that are again in a different color.
It's almost like it was a feature to allow you to view the changes you made today, versus the ones you made earlier.
I'm reviewing a document someone else wrote, so the origin of the document (in terms of which version of Word was used to create it) is not known to me, but I suspect it is Word for Windows and an earlier version of Word as well. One clue is that it is in .doc format, not docx.