Good wok on the photo.
For Vista and Saga... steel painted, money island etc were all painted green.
Any old photos of the Boat Deck and Bridge Deck? Quite possible they were TEAK decks. If not, go for green again. If the decks are teak, then scuppers and trim would also be green.
Hull colour. NAL grey is not a standard grey... and not just black with white or even blue/black with white. NAL colours was more a tan shade of grey.
Here is a photo of Sagafjord in NAL colours. It shows the funnel buff and the hull grey. Note. If you have photos of the ship is Cunard livery, the grey they used as a different shade. The photo of Vistafjord in Cunard shows the different grey.