I think that the Ford policy of 'you can any colour you like as long as it is black' applied to the aeroplane too but not, of course, black but aluminium or silver dope. My reckoning and memory of pictures in a Profile Publications I still have, shows that all Ford 3m s were bare metal. But not so multi panelled like post war jets more of an even overall finish. They may have been aluminium painted but not ever seen any 1930s period Fords in any other colour. The odd post WW" restored ones would have acquired a predominantly white with personal trim colours. But for your needs an aluminiu overaal finish woyld be pretty much correct. I have a part built one passed on to me that I plan to finish one day as the only RCAF one pre war and that was the same colour other than markings.
Hope this helps.