Pedro,
i was not going to answer since i am not an expert,
but since no one else has replied, i will give you what i have:
i believe (there's a reassuring thought!) that at the time of Battle of Britain,
the grey would have been the most likely base color for the Flak.
i don't think the dunkelgelb was common until around '43.
i am not sure what you mean w/ the rubble part of your question.
if the Stuka is 1/48, what scale are the vehicles & gun?
also 1/48, or 1/35?
if they are 1/35, are you doing a 'forced perspective' w/ the plane in the back ?