Personally I have no redheads in my family (only blondes and brunettes) and I must say that my observation is that redheads are more rare in Slavic populations than in Germanic and especially Celtic ones, but still visible.

In Poland one sees them everysooften (you can now also comment on this, Svaty ;)), but they are not obviously near as common as blondes and brunettes are. Not sure how it is in rest of Slavic countries?