According to a buddy that worked in the St.Louis plant and said he had the actual carpet install job at that time (71) all 4 speed cars got black carpet.
It had been brought up at one of our Wednesday evening guys night because on of the guys has a 71 GTX B-5 Blue with a B-5 Blue interior, U Code, Air Grabber 4 speed car with a blue interior with black carpet. (The car still had the original carpet in it when he bought it in the 90's).

He said automatics had different colors that matched the interior, but 4 speed were all black carpet.

He hired in back in 1967 and just retired from Chrysler a few ago, when they closed the plants here he transferred to a PDC (Parts Distribution Center) in Dallas. Almost 50 years at Chrysler.