fair in this context refers to paleness basically. though, it’s often meant in the same way that someone today might say “she’s thicc” and just mean “she’s attractive” in a more general sense. fairness meant beauty to European high society at the time. aside from the obvious racial connotations, it also implies that she has spent very little time outdoors and has been free of disfiguring diseases, so high of status. it generally carries a lot of implications beyond just “white” and “clear skin”. it captures everything that a European nobleman of the time would find attractive in one word.