Happy to see this thread back on track, finally! Great.
I actually think it's alot simpler than you might think. If you look at these two characters, Sawney and Whatshisname:
I think we can agree that these characters are meant to be black right? Despite their features.. and that's what I want to go to.
I believe it could easily be done, however the characters could be considered old models. Remember how Yugirir was first introduced with a Miqo'te model? Or how we never saw Miqo'te children until a certain point(still have yet to see Miqo'te boys)? Or Au Ra children? Until certain time in the game's life they either didn't exist or looked different until they were fully animated. We have many Hyurs out there with unique faces that aren't playable in Ishgard, Gyr Abania, and Othard.
I think this could be a perfect example. Say Sawney is a beta or alpha version. It wouldn't surprise me at all if they eventually made a character that is black but looks different. A more complete or up-to-date character. Their origin? Who knows honestly... But that's for SE to answer!
This goes for Male Miqo'te children, Roegadyn children, various mixed races, Lalafell children(under 12) and more. I swear those people must hide in the best spots for them to go undiscovered for so long.