They are a special breed of chicken.
See Silkie - Wiki: http://en.wikipedia.org/wiki/Silkie_(chicken)
They have silky feathers and are often kept as pets in the west. They are raised in Taihe province in China and are sometimes called Taihe chickens.
There is a bit of info on CHOW: http://www.chow.com/ingredients/127 .
As for how they taste, I'd say not that much different than a regular chicken. Maybe a bit richer. I have only had them in soup and that seems to be about the only traditional preparation. The soup is considered medicinal and is made with bitter gourd/melon as well. The Asian grocer near me sells the chickens whole and split in half and wrapped up in bundles with the rest of ingredients for the traditional soup.
I would be interested in roasting a whole bird just to find out what it would be like and I might just do that sometime. The flesh is almost purplish and the bones and skin dark charcoal to black.