Thanks GG,
I believe you are correct about the upper walkways on The J models but the wing appears to have a slightly darker gray walkway. I may have found an answer looking through an old tech manual for painting and marking the Phantoms - NAVAIR 01-245FDB. It states the wing walkway area is to be primed with non-slip Corogard and painted using Light Gull Gray Corogard (Lists color code as M49AC19 which I believe is FS36440 Light Gull Gray?).
Now I'm trying to figure out exactly what shade of gray was used on the aircraft upper surfaces, was is FS16440 Light Gull Grey?