Hi Massimo,
I have tendency to make colors on the planes low vis and as simple as possible, especially for planes from that time. Galchenko removed big red stars from his plane. Why would he added something else red on his plane?
I would say it was repainted by some sort of green, or mixture black&ALG-1. It is visible on the several screenshots, so it is not a defect on one particular photo.
However, it is visible only (on the left side) on the winter photo, not on the right side on the summer photos. So it was there problaly only during a short time period and it disappeared when winter camo was overpainted.
May be it would be good to check the sentence of the photos. It is apparent that black and dark green blotches changed their appearance during the time.
Here the lighter area on the horiz. stab reaches only to front edge of the rudder:

while here it reaches much further and hat different shape:

Regarding the winter camo - two white blotches on the left wing I would move now (especially that bottom one) more to the right, closer to the wing root to align them with the black/green area, not leave them like in my original picture:

more like here:

Regards,
66misos