Thanks Dennis, that is very helpful and interesting. Ian Huntley I have heard of. I think he produces the paints for White Ensign and perhaps Xtracolor as well.
Xtracolor X133 is Neutral Gray FS16270 and more similar to Medium Sea Grey than Ocean Grey. Ocean Grey was chosen because of its blue cast which made it suitable for camouflage at higher altitudes. A lot has been discussed about the US substitute for Ocean Grey. It is said to have matched Dark Sea Grey and indeed some modellers have used DSG to represent ANA 603 . Xtracolor have a large number of greys used by the US Air Force/Navy which helpfully they list with FS Numbers. They call FS16118 Gunship Grey (X130). Xtracolor’s Ocean Grey (X6) certainly has a blue cast, more so than Humbrol’s version H106. Gunship Grey also has a blue cast but less so than OG. It is similar to Xtracolor’s DSG (X4) but not identical (bluer). As Gunship Grey is somewhere between OG and DSG. I can accept that it was the colour used as a substitute for Ocean Grey. I cannot see Neutral Grey being used in place of Ocean Grey as it is far to pale. Also it would be obvious in photographs. There is no Humbrol H176. I haven’t found it listed as discontinued either. Perhaps it existed in the far past or maybe it’s a misprint for H126 US Medium Grey.
Xtracolor X137 is Light Gull Grey FS16440. Again the problem I have with this is it is far too pale a grey to have been used as a substitute for Medium Sea Grey. The difference between ANA 603 and OG has long been noted and discussed but nobody remarks on any difference between ANA 602 and MSG. As there is a much greater difference between LGG and MSG. than between OG and ANA 603 I would expect there to be some comment about it. Again it would be very noticeable in photographs. Whatever colour was used in the US as a substitute for MSG I think it must have been very close to MSG.
This German site shows ANA and FS colours. http://www.pmcn.de/weO.htm
I am always wary of colours on computer screens but this site shows ANA 602 Light Gray as a darker grey than LGG FS36440 and more like MSG. Here FS16118 is called Dark Sea Grey.
The only manufacturer that I have found that makes a colour specifically described as ANA 602 is the Czech company Agama. http://www.jadarhobby.waw.pl/agama-c-21_453.html?page=3
Again it is a darker grey than LGG. Unfortunately neither of them gives an FS number equivalent.