Good question Tracy! The relevant AFOs relating to the non-slip deck paint used by the RN at that time are AFO 1895 of 1938 and AFO of 2859 of 1939. As you can see, the non-slip deck paint was supplied by the International Paint and Compositions Company in a range of colours and a distinction is drawn between Home Fleet grey and dark grey.
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Given the relatively narrow range of paint colours available to UK industry in that era (the British Standard 381C range) we can speculate that the “dark grey” non-slip deck paint was BS 381C #32 in colour. This was a neutral grey without the blue element that Home Fleet grey had in its mix.
Jamie can confirm this, but based on our research that is why he offers a non-slip deck dark grey in his NARN range that is different to his Home Fleet greys. He offers two tones of Home Fleet grey, one at 10% RF and one at 13% RF, because that range of RF (10% - 13%) for Home Fleet grey is what is recorded in the files. Quite why there is this variation we do not yet understand.
I suggest that 507A itself would not have been used as a
non-slip deck paint although it might have been used on horizontal surfaces where people did not routinely walk. 507A was just a formulation of ingredients that arrived at a less glossy version than 507B of the colour Home Fleet grey. We have discovered that there were other formulations used by the RN and RAN to achieve even matter still finishes of the colour Home Fleet grey.
In many cases where people write 507A what they really mean is Home Fleet grey.
But in a nutshell, in 1939, if you are looking at something dark, you could have had a deck painted in non-slip dark grey or non-slip HFG (of whichever tone). On your model it’s your choice based on assessment of B&W photos or intuition! (And don’t forget the black option either.)