Ralph, don't worry too much about the overall colour finish. There are too many factors when viewing colour and B&W photos of the actual aircraft, whether period photos or the RAFM example. Such things as exposure, colour balance, lighting etc, when the original photo was taken, and then reproduction on the printed page or PC monitor all have an effect on the colours, tones etc etc.
Add to that when the photos were taken - sunny day on Tuesday, aircraft not flown for three days. Dull day the following Tuesday, and aircraft has been out in the open after a couple of "Ops" in poor weather, etc etc.
Also, the Defiant wasn't in service as a night fighter for very long, or indeed in service in general for that long anyway.
Then there is the "scale effect", where the physical size of a model may determine what colour is actually used. Should it be black, blue-black, dark grey etc, when one colour may look fine in one size, but totally. wrong on another size, due to the eye seeing things as we "expect to see them".
Just get it to "look right" without worrying too much about total accuracy as, let's face it, there's no one around now to say "that's wrong, It should be 0.0005 % lighter or whatever.
With a multi-colour scheme, things, of course, would be different, especially if photo evidence of a particular subject aircraft shows various areas of fading, patches etc etc, but with an overall single colour, especially matt black, then a "general representation" is all that is needed.
The pic below shows my 1/48th scale Beaufighter built around 16 years ago, and brush-painted with various "shades" of black to represent the same colour scheme used when the Defiant went into service as a night fighter around the same period.
Not perfect but acceptable.