brent But nevermind the corroboration: it doesn't even launch---
Just another data point ... it launches fine here, and is quite black also. (Materia-Dark)
Note the libEGL warning, though. Perhaps a clue? I started that without elevated credentials. When I started it as root, the results were very different.
There were a LOT of instances of the error message you see here, and the control center is no longer black.