Red violet pak choi is one of my favorite 'greens' this fall.
I keep trying to take pictures of it, but it just doesn't seem to be very photogenic.
It's a hybrid in the B. rapa narinosa group of the brassica family. It's cold tolerant and a vigorous producer. It has spoon shaped leaves that can get pretty big (as big as my hand for example). Leaves are always mild flavored, and tender, at least when grown in a greenhouse like I am.