Hi all,
a friend is making researches about the colors of paints utilized by Republican planes, SB in particular, during the Civil War, and on colors utilized by Nationalists to repaint the captured planes after the war. He is starting to work on profiles of SB.
There was some interesting discussion there, some years ago: http://massimotessitori.altervista.org/sovietwarplanes/board/index.php?topic=1019.0
I have some photos of the museum of Madrid too, but they were repainted after the war and the authenticity is not guaranteed.
In general, we have seen samples two shades