The “Redskin” moniker never had anything to do with the color of the actual skin. It had to do with a cultural practice amongst the tribes of certain regions using red skin paint amongst their warriors, which made their skins red. So it referred contextually specifically to their warriors, to the tribes or cultures that raised such warriors (particularly in the south-east and middle atlantic), and to the peoples as a whole as differentiated from Europeans - as when the term arose Amerinds were considered to be white.
Go back and read the old documents, treaties and such. The term is used by the various European and American entities to ‘suck up’ to the tribes. It wasn’t derogatory to anyone except for about 50-60 years at the end of the 1800s until mid 1900s.