A: Gabriel Reyes has Hispanic Heiritage, but was born in Los Angeles. So he's not Black, but at least to a degree Hispanic.
B: On the official Overwatch Site, in Reaper's Character Despriction it is said that because of what Moira did to him with her Experiments he's constantly decaying and regenerating. So by that Logic he shouldn't have a proper Nose or Ears anymore AND lost all of his Picmentation. You can even see his gray-ish white Skin on his Default Design around his Bicep Area. So imagine Reaper looking kinda like Marvel's Redskull in the Face (and probably fairly boney for the rest of his Body too) with gray-ish white Skin.