So what's the difference between them? I took pictures. Look.
I'm guessing both companies use some kind of black pigment for both. One's a hell of a lot greener than the other, obviously. However, S.T. Black does have a slight greenish hue, though on the whole it appears very brownish under most lighting conditions. This reminds me of one time in high school art class when I was mixing black and white paint together. You would think I would get gray paint out of the mix, but no....I got some fucked up chartreuse green. It may have been because of my Alice in Wonderland luck or because of the excellent fine arts department at my ol' high school where the track coach was also the art teacher. He was a real character, as are all high school teachers, and had no artistic ability or critical eye. His only direction to us art students was "You should put some more glue on this" or "Let me put some glue on that." On second thought, maybe I actually did learn something from that class. Excuse me while I go put some glue on some latex.
S.T. Smoke and S.T. Black photographed over a white background: