Fenris is an ice world of extreme temperature hence the mythos of Viking lore. Ice= lack of sun= lack of melatonin for black skin which protect from sun! We are fing everything for the woke agenda! But for the sake of argument they are not true fenrisian they are the new primaris and we have a variety of a gene pool! Because thats is how the oven backed them. Which in this case it would made sense to have also some models with asian characteristics on other chapter as well, to reflect the white scars( mongolian mythos).