I think I'd say what I'd learned was not that there is no truly black glass, but that most of what we call black isn't really. For instance, a Marble King bumblebee with purple ribbons. We just naturally call them black -- confusing new collectors along the way.
There's some Akro which seems totally black to me. If it's really something else, I don't know it yet. I'll gladly keep calling it black.