A remarkable proportion of the old Russian aristocracy was descended from Mongol/Tatar ancestors. There is a very interesting bit on this, analysis of names and ancestries, in Orlando Figes, “Natashas Dance”.
Peter the Great’s mother was of Tatar origin and Lenin”s father was a Buryat Mongol.
I had heard that many Russians are said to have “Mongol eyes” or “Tatar eyes” that are almond shaped even though blue.
This could explain it. Of course, thanks to John Wayne we now know that Genghis Khan had blue eyes.
;^)