(Phil Morris, Smallville and David Harewood)
The Justice League features the best heroes in the DC Universe, but they had a green alien as a team member long before a black character actually joined their ranks.
And even in his alter ego of John Jones, Martian Manhunter was a white detective.
The Smallville showrunners realized that was an easy workaround and brought in the talented Morris to assume the role. These days, Jones is more commonly portrayed as a black man.
That held true with Supergirl where David Harewood has taken up the mantle of J’onn J’onzz with far less fuss and issues over his skin color. It’s almost the norm now that Martian Manhunter is played by a black man as Zack Snyder has heavily suggested Harry Lennix will have his Man of Steel role expanded to reveal he is the Martian Manhunter in this universe.