What I've seen & owned since these cars were new agrees with 6bblgt EXCEPT for 1 thing: my Decor '69 RR 4spd HT (green Satellite interior) did come with black carpet. (St Louis, midyear Spring Special car.)
I think the buckets/console option and higher trim levels (GTX) would move the spec past the black carpet as some have indicated here & on previous threads. I'd like to see pics of ORIGINAL RRs with consoles, 4speeds and green, red, tan & blue interiors, and any RRs with 4-speed & colored carpets.
My guess is that the black carpet was a cost-control measure - as 6bbl suggests - for the "lesser" trim levels. Chrysler probably a better deal on 20,000 of the same thing than 5,000 of 4 different things. People shopping the higher trim levels wouldn't be as happy with non-matched carpet.
I'm sure there were exceptions/mistakes built, but if 99% follow a common spec, that's probably what was intended.