Durpari aren't black, they're dark skinned, but not what we (Real world people) would call black. If we saw a Durpari we would think they were from India.
But yes, Turmish is black, and a good way to add racial diversity in the Heartlands for your players without having to go to Chult.
Well, I like the idea of other "real world" cultures getting time in the Forgotten Realms. Medieval Europe, Asia and etc get their spot; so I made an effort to find a place for a warrior named Aja Sakumbe to hail from.
The area of The Shaar is the answer I came up with. To me, the Border Kingdoms were a fine example of colonial powers setting up on the edge of what was once the predominant domain of peoples much like the Zulu.
It fits for us.
That is what I love about the vastness of the Forgotten Realms, wiggle room.