Coincidentally, I visited the Singleton Infantry Museum yesterday. I photographed a lot of rifles, machine guns and anti-tank weapons. The furniture comes in furniture colours. I'd say, whatever you do, don't stick to one colour. I read a book recently about the war in North Africa, from 1940-43, and it referred to the colour of the rifle butts, because Australians used new rifles with honey-coloured stocks, while the British used rifles from WW1 that had been stored in grease, and were much, much darker in colour (possibly simulated by an oil wash?).
Will upload pics of guns later and advise somewhere of their location if anyone's interested in photos of 2pdr, 6pdr, 17pdr, PaK38, Panzerschreck, Nordenfeldt, Maxim, Gatling, trench mortar, grenade thrower, and firearms from the C19th to today.