^^this!
I have a black horse who has one of the very cliche names mentioned above. Because of his full name I wanted to rename him Elvis or Presley but was told it was bad luck. In hindsight I should have just changed it!!
I've got a completely black gelding called Harry. Clearly, nothing to do with his colour! His dam was called Harriet though, so obviously. . ! His race name was Capall Dorcha - I believe its gaelic for The Dark Horse.
Onyx - mineral
Obsidian - mineral
Deneb (brightest star in the constellation Cygnus. opposite association to white Swans, just so y'all follow!)
Magic (prefix with black if you wanted I guess)