Hi Massimo,
thank you. Regarding colors here are possible alternatives from
http://massimotessitori.altervista.org/sovietwarplanes/pages/colors/color-table.html“Zashchitnyi”* khaki , Upper surfaces - metal (TB-1, TB-3, R-6) or fabric/wood (R-5, U-2), 1927-1937
3B dark green, oil Army paint, sometimes used on metal planes (TB-3), 1933-37
AE-7 (zashchitnyi) gloss camouflage green, overall uppersurfaces of metal planes, Oil enamel, Specification issued in 1936-37
"My" plane was during VVS already several years old, so paint could be weathered or whatever else. It is something between khaki and dark green, looks like darker AE-7 sample.
Regards,
66misos