4-speed RRs got black carpet, regardless of interior color, in '68 & '69 and likely '70.
All of my 4-speed '68-'69 RRs were that way - original cars - whether base or Decor Group.
My Decor Group auto '68 RR coupe had a burgundy-color carpet.
My base-interior auto '68 RR coupe - blue interior - had a blue & black speckled rubber mat.
I've also owned '68-'69 4-speed RRs with green and blue interiors, all had black carpet.
Carpet color on auto RRs is about the darkness of dash & package tray.
Never seen an option regarding carpet on those cars.
It's possible that a dealer might upgrade that at customer request, but I've never seen a documented example.