I wonder how much of this is an east coast/AT thing. When I lived in California, many minorities used the local parks and recreational opportunities and I know that was the case, to a lesser extent, even in Yosemite. On the JMT, I did see minorities. Not nearly as many on the VA, MD, and PA AT sections I have completed to date. I do believe that access exists to the AT that is better in many ways than out west. So it could be a cultural difference. Local parks here near DC are also abundant. I can walk outside my building and be on an actual unpaved hiking trail in ten minutes.
http://www.nps.gov/pohe/index.htm. I hardly ever see anyone on this trail, minority or not, if I walk a mile or two upriver. Feels like wilderness even though it's obviously not.