It's nicely done, but I agree that the 'green' looks a tad Luftwaffe-ish. Is it possible to rub a little green in there with a fine sponge to change the tone a bit, whilst retained that weathered slightly-unwell look ?
I sometimes use a small sponge (came with an acrylic painting package) to rub in darker or lighter tones into the base colour for a weathering effect (but not the edges, where colours meet..). That said, with British Summers it's not unusual for all colours, and the Sky, to take on a
a greyish tinge after weeks of rain

"Get your facts first, and then you can distort them as much as you please"- Mark Twain.