What are the 2nd and 3rd most common ethnicity among hobbyists?
And what cities do providers see the most diversity among clients?

THe question should be...why are so many white men on TER and seeking Providers?  HUMMMM

black is the second most common (in the south), in others Latino (especially in the southwest), and in others, perhaps Asian (west coast).  

Melting pots: Boston, Chicago, DC, LA, Miami, NYC, Philly, SF and Vegas.  

Although race is important, the next step would be if your bold enough is to come out with the survey with respect to income and disposable income on the hobby.  This is where you will get the real demographics on what the actual break down is. Also pay attention to the color of collars and the region that they are from. Finally look at the population density of the places most frequented by providers, that will be a more telling statistic as well to.  So although race might be important, it is stratification that would control, predict and obligate this discussion.