It was relatively dark in there because of the black leather walls and black carpet but well lit - if that makes sense. The lighting gave it a warm, luxurious feeling which is appropriate with this being the first class stairway that primarily served the first class cabin decks (1-3), the first class restaurant (Columbia) and the first class entrance to the ship, the Midships Lobby. The Grill Room Bar/Grill Room, the high end One Deck Shop and other first class locations were just steps away too.
The carpets were a different texture than the walls but both were black (Navy blue?). While a bit difficult to enable in the model because of lighting limitations, the texture difference and the angle difference (step risers and treads) made it easy to distinguish the step edges. At least it did when I was a teenager. 45+ years on, I might have a bit more difficulty. I sincerely doubt this color scheme would ever be reprised today due to present day safety and ship emergency egress constraints.