The only true grey uniforms I can think of is the leather jacket and matching trousers issued for bad weather. I couldn't give you an exact FS number or anything like that, but at that scale I would assume a semi-gloss look.
If the jacket looks like the army issue style, it would be field grey but with yellow or gilt buttons, badges and lace. This uniform though was issued only to land based units, such as coast artillary units, but in later years it is possible it made it's way into the navy proper.
I do have an illustrated colour plate in front of me entitled KHAKI SERVICE UNIFORM and states that it was recovered from submarine personnel operating in atlantic waters. The figure wears khaki coloured shorts and a long sleeved shirt that is slightly lighter shade of khaki. It adds buttons would be either gold or brown (depending on rank?) So here I suggest either khaki or fieldgrey shirt would be okay. Hope this helps some.
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Jack