I'm a waittress that wonders why black men and women don't tip me even if I provide them with great service.

Every time I have a table with black customers, I begin to feel a little depressed because I feel like I'm waisting my time waiting on them. No matter how courteous I am or how attentive, I feel like they are out to make me feel like I'm not worth a dime. The last time I was tipped by my black customers, I ran outside after them and thanked them excessively because I wanted them to know how much I appreciated their tip. I sometimes wonder if black people hate asian women and will do anything it takes to discriminate or dis us, but even my coworker who happens to be a black american woman doesn't seem too happy to have black customers. Please answer this question that has been in my head for four years.