I used the old Snyder & Short colours initially including 507A for the steel decks.
A letter exists from Capt Tennant describing the camouflage on Repulse in which he described the tones as a very dark grey and a grey between Light Grey and Dark Grey which he then likens to some paint mentioned in another document dating back to the late 1930s. I've had a complete hard drive failure on Christmas Eve and lost a large amount of stuff so I can't verify his exact wording right now but I am sure dick can verify for me.
I interpreted that to mean that the lightest tone wasn't 507C but an unofficial shade with characteristics as described - between Light Grey (507C, 45% LRV) and Dark Grey (aka Home Fleet Grey, 10% LRV).
This model thus sat on the shelf of doom for some time but a few weeks ago I decided to just wing it but with the benefit of some numerical data.
The lightest tone on the model is the old, incorrect 507C which is too light at 52% LRV - this is the same shade all other brands copied - FWIW. The tins below are from left to right the corrected 507C at 45% LRV, BS381C-637 Medium Sea Grey at 28% LRV, old Snyder & Short "AP507B Medium Grey" (which you'd think Capt. Tennant would have made reference to instead of describing something as between 507C and HFG if that combination of shade and nomenclature did infact exist) and the corrected (lightened) 507A at 10% LRV. The Snyder & Short 507A measures out at 8% LRV by the way.
I chose Medium Sea Grey for my model. The darker tone is/always was painted in RAF Night (bomber black) as I felt matt black was inappropriate on a model.
Here is how it is currently looking. I think this will be an impossible subject to ever resolve categorically, but I am pleased with my choices here and they do resemble the photographic records nicely whilst not contradicting Capt Tennant's narraritive on his own ship.