NIce stuff Andy.
The first digit of the FS number means a kind of the colour finish. 1-gloss, 2-semi-gloss/semi-matt, 3-matt.
Yes, that's why I mentioned to Geo that the FS23538 would be glossier than 33538.
Geo, I took a look through more of my references but the vast majority of my discussions with experts on RCAF colours was devoted to the DE/DG/Sky scheme that we are depicting on our Canadian-manufactured Hurricane. In attempting to establish actual colours of vintage aircraft, the absence of actual artifacts combined with, in the case of Canadian manufacturing practices, a lack of colour chits, makes a true determination of colours problematic.
Generally, Canadian manufacturers were obliged to paint their aircraft in colours either matching or appearing as close as possible to British Ministry of Air Production (MAP) standards. There were a number of suppliers of paint to the Canadian production facilities; International Paints (under license by the British manufacturer, Titanine), Thorpe-Hancock (manufacturer of Cellon paints), and Berry Brothers are but three and you would be hard pressed to find paint chits for any of these companies (if you ever do, LET ME KNOW!). Even if you could get an actual paint chit, you would still need to determine which supplier provided the paints to the factory that built your bird. I do have an electronic scan of a Titanine standard colour chart but a) it is a scan, and b) the original is yellowed so an attempt to exactly match a historically accurate colour based on this chart would be futile.
As you can appreciate, this all gets very subjective and I'd suggest that, despite your best efforts to get an answer for the best match, you will not end up with a definitive, fact-based answer. Personally, I would lean toward the colour referenced in the article that I posted above and mix your paints as close as possible to the FS23538 standard as you can. The answer to any critic who torments you about your choice would be to have him 1) produce facts proving which paint supplier provided the paint for your bird and 2) produce an original copy of the paint chart used by that supplier. That should shut him up.