I’s guess the reason someone thought negro was an acceptable term is that it means black.
I once publically humiliated a blowhard liberal spouting off how negro was word invented by English slave traders. It was in the middle of our design studio. I pulled a box with an India Ink bottle inside. Slowly rotated so each side became visible to all. Labels were; black, noir schwarz, and negro. Man never forgave me. It’s a good thing.