Hi Martin
I've got a fair selection of colour photos of WWII cockpits - admittedly all museum examples (and too obviously copyright to risk getting the site into trouble by posting

).
There does seem to have been a little variation; most RAF gunbuttons are brass, in a brass surround. A pic of the Hendon Typhoon shows a dull siver button in a brass surround, while the BoB Memorial Flight Spitfire MkII has a brass button in a black surround!
Hope this helps and oops! almost forgot... tasty looking office! I particularrly like the Sutton harness!
Rowan