it could be that the older planes were repainted with the newer colors, so the relation between colors and year of building can be altered.
According to Hormat, in this period, old painted aircraft were not repeinted...
We know that this happens in 1941 with the adjonction of AMT-6 color.
I have to say thet most of type 5 in the pics seems darker to me
Alex my Russian Friend is ending the translation in french of the Orlov paper, and it seem full of information...
Massimo did you get an english translation ? Konstantin you read it I suppose?
Xan