Following in line with blue, white, and pink collar workers, this phrase has popped up to describe the new model worker of the American workforce. The Black Collar Worker is the new innovative, entrepreneurial worker — the one that cannot be outsourced. The name is a play-off of the current paradigm of the movement, Steve Jobs, and his black turtlenecks that he wore.
Interestingly, the word used to be associated with miners and oil workers for the coal and oil on their clothes, but it has been co-opted in recent years. Wikipedia has an interesting list of all of the different types of collared workers.