When presented with a new musical technology, the first question that occurs to a certain sort of mind is “what happens if I press all the buttons?” People used to do this with pianola rolls (particularly Conlon Nancarrow and his studies for player piano); now they do it with piano-sound synthesizers, controlled by hand-tweaked MIDI files. “Black” because that’s what the manuscript rendering looks like.
The current wave was started by kakakakaito1998 on YouTube; now it’s a scene. Unfortunately, much of what you hear in the result is artifacts of synthesis; it would be interesting to hear some of these on a physical player piano.
Update: Of course, some are not fans.