I live in NP country, where the Four Aces ran regularly. That sure is an odd color on 2626, I don't think it was ever painted grey
Au Contraire!
The Sunset models of Four Aces are on their way and look spectacular in Timken Brewster Green, NP Black and NP Grey.
The NP was fond of Gray boilers and cylinder jackets for passenger locomotives. Several other Northerns and some Pacifics received grey paint as well.