Hi Massimo,
yes, I guess this could also be a very faded and discolored green (especially when you look at the dark green folded corners on the backside) but to me the topside also looks almost exactly the same as Akan's AMT-1 used by xan in his Po-2 build here: http://massimotessitori.altervista.org/sovietwarplanes/board/index.php?topic=1585.15 (reply #28, it even matches the template). So I am torn..
(Another paint I have here and which looks exactly like the color in the relic is, funnily enough, AK Real Color's 061 Dunkelgelb 44).
Anyway, it was just a thought. I should have a look at these pieces on a different monitor..