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August 1942, Corpus Christi, Texas: "It's an intricate operation, installing a 30-caliber machine gun in a Navy PBY plane, but not too tricky for Jesse Rhodes Waller. He's a Georgia man who's been in the Navy 5-1/2 years. At the Naval Air Base he sees that the flying ships are kept in tip-top shape. Waller is an aviation ordnance mate." Kodachrome transparency by Howard HollemView attachment 510286
Strangely enough, only the right side of the the photo was colorized. That's why it seems to be grey I think. Correct me if I am wrong.
I think it's an original colour image.
But see the lowest window on the blister. Take a look at the forward edge. Just behind the leading edge is goes from blue to grey back to front.
I think it reads F3178, but cannot be sure. But the back of the aircraft is blue. Not grey.
It may appear blue to you on your display whereas it may look entirely different on my display. I'm not going to argue over what you can see or how you interpret the colour.
However, the standard RAF upper surface camouflage colours for flying boats for much of WW2 were Dark Slate Grey (which, ironically, had a green tone) and Extra Dark Sea Grey