You're right: the shop probably would act the same way with most of us regardless of our color. But American Blacks are indoctrinated to see any little affront as racism and nothing else. That's why they may never be able to mainstream.
Its horrible but that is the case. Its even worse when politics is brought into it. The same folks who claim they don’t want to be judged on skin color, orientation, and gender always seem to reach for that crutch to hit people with when they don’t get their way and suddenly its all about them being black, gay, or a women.