I honestly think this is a self-segregating issue. I have known many farmers, ranchers, and practical gardeners of African descent. I just don't think - like most ranchers, farmers, and gardeners of any ethnicity - they tend to think of what they do in terms of permaculture. I also think we (as white people) tend not to go out of our way to invite different types of folks into our permie circles. It's not a criticism; I am noticing it for myself. I have been in many hobbiest groups and have seen/experienced the same thing. Trail riding is another one that seems to self segregate. Quilting too...of all things. It's very interesting, and something I am now committed to changing.