Why black? No reason was given when the announcement was made. But many people believe it’s due to the numerous empty red seats being clearly visible on TV in those premium lower level middle sections. The black seat covers mask the emptiness of the arena on TV a lot better, as will the all black seats.
https://www.mlive.com/sports/2019/03/first-look-new-all-black-seats-installed-at-little-caesars-arena.html