Ah, but that goes for the Ligonians too. They are aliens played by African American actors, like the Tamarians. If the Tamarians are not black, then neither are the Ligonians.
Sonic, what is the color of the Tamarians' skin? And what color is the Ligonians skin? Whatever defense you may bring up regarding the Tamarians, I guarantee you they were not casted because they had black skin. And compared to the Ligonians, the Tamarians are far more civil with Darmok actually beaming down to the planet with the Picard, giving him his own knife, sharing his fire and forming a friendship through understanding. The Ligonians?
"As you can see, Captain, you may excel in technology, but not in civilized behavior."