Here is just a few of his works. There are a lot more.

Actualy slavic people had only blond (many variations from light blond to dark blond) hair and light eyes. If you see dark hair or black eyes it means that that person has a foreign blood in him, that’s all.

As a Russian I can tell only for Russians but even now, I can clearly see “that” typical hair colour that we traditionally call “rus” around 70 % of people I see in the crowd every day as I take subway to go to work.  Especially it can be seen in men as they dont dye their hair up as most of women do.