I think I might have solved the "cut-pile" or "80/20 loop" carpet mystery
Very interesting replies. I had a twin to the red '73 Dart Sport above and it had black loop carpeting. The '69 Dart sedan I owned for a while had black loop carpeting. The '74 Valiant I owned which was a fairly loaded car had green loop.
Here is the cut-pile in my Valiant. Presumed to be original based on the amount of fade and the sewn-on heel pad.