Roxelana

It derives from the Italian word "rosso/a", meaning (in the context of a person) "ginger-headed", "redhead". It's not Ukrainian, nor Turkish, nor Ruthenian - as far as I know, the Venetians came up with that name. That's why in 'Magnificent Century' Hurrem/Roksolana is red-haired.
However, all of her portraits picture her differently, and frankly most were painted even after her death, so it's hard to tell how she actually looked like.

From a Turkish nickname meaning "Ruthenian" (I.e. Ukrainian). [noted -ed]