Black is a fashion designer and model, who specialises in making punk and goth themed clothing. Her clothes are very popular with a lot of ponies too, and she has various stores across Equestria.
She has trouble with expressing herself and her feelings, often coming across as more stoic or annoyed then she intends to do, which she feels bad about. She does want to get better at expressing herself more.
She is also very fond of using black in her clothing too. LOTS, of black x3