I think that is a bit of a stretch. There is concrete evidence that explains this happens a lot, and it's clear that racism [1] and sexism [2] are a key part of it.
And -- not as scientific here -- but there's intuition I have gathered that's backed up with 10 years of extensive dining out in various arrangements and settings, and anecdotes from my server friends about the politics in restaurants.
[1] http://tippingresearch.com/uploads/Business_Considerations_T...
[2] http://tippingresearch.com/uploads/ServerAppearance1-3-08.pd...
I was saying that there are times that it happens that have nothing to do with skin color and would happen (maybe the waiter is having a bad day who knows) to anyone.
Like the man in the car next to me (assuming he is not gay) if I was a hot girl I would automatically assume it's because I'm a hot girl. Of course this is not the same as saying that men don't look at a girl in the car next to them!
Of course that's a possibility -- servers have bad days, sure, but these isolated incidents don't negate the need to solve the bigger problems of wage disparity in restaurants (cooks being paid half what servers earn -- close to minimum wage in some instances, no matter that they went through culinary school and incurred huge debt), the problems of racism and sexism, etc. I feel non-tipping is the easy and obvious solution here.
Likewise sometimes I am in my car and someone looks over at me. I think "wow if I was a girl I would think they are looking at me because of that!" (Because I tend to check out girls!)
My point is although there is no question you are subject to the actions you (and others describe) but it also could be the case that it happens for other reasons that have nothing to do with skin color. Make sense?
Lastly, while I am white, I am of a religion that has a percentage of the population that is biased against us. But for some reason I haven't really experienced that bad treatment that I can link to my religion. I think this is because my last name doesn't scream the religion as some others do.
One more thing. I'm married to a physician and I dated a physician. And when we are together people always assume I am the doctor or also a doctor. And they always seem to defer to me rather than my wife (or in the past girlfriend). My wife also has been treated by nurses without respect something they don't do to the male doctors.