Natural black hair in Poland?

My friend is half Polish and half Norwegian. She has natural jet black hair, white skin, grey eyes. But how is it possible to have that type of hair color when she has those two ethnicities? She told me she does not dye it, and that many people have asked her about it as well. She explained that it probably comes from her Polish side of the family. Her mother also has jet black hair but her father (who is from Norway) has dirty blonde hair.

Is this rare or common, because I thought having natural jet black hair in Poland would've been impossible?

Thank you in advance!

who cares about this obsession with colouring really?
Maybe her grandmother shagged a gypsy?

Of course it's possible, plenty of southern European blood in Poland, mainly Italian.

oh wait....maybe her family were Polish Jews?...:)

That's another option.