Hi!
I totally agree with you Arek, in my first intervention in this thread I suggested to use Humbrol 30 as a "possible shade".
Yes, Balillas built in Poland were delivered in 1921, before them Poland received examples from Italy.
Now, looking at the famous lineup photos of Kosciuzko Squadron on snowy airfield, we know that No.1 was green, No.2 was natural wood clear varnished, No.3 was green again etc. I may imagine (hope?) that the dark green choosed to paint the green ones was the same for all. Yes, it was the dark green they have in hand (maybe the one used for armored cars as Ford Tfc?).
I don't think that we can state about the perfect shade of this green, maybe some polish historian or researcher can?
Cheers,
Roberto