I have found that over gloss black enamel, 3 coats lightly sprayed on gives a nice dark look to it, like on the rear fuse of my 104, then I mask those pannels off and shoot 2-3 more light coats on to bting it to a nice light color.
Not sure if that would work for duraluminium…
I have to use airframe allu over gloss black for mu mustang as my local Alclad supplier doesn’t have any duraluminium 
cs.finescale.com/…/160670.aspx
scroll down a bit
Theuns