Did jack Johnson drew a color line himself?
For a guy who fought for his right, or for that matter, a black man's rights to contend for the world heavyweight championship, he surely didn't defend against the other outstanding black men of his day and the sole exception was Battling Jim Johnson who is not a good as any men mentioned below.
The question here is why?
Is it money with fighting against white challengers? Or he knew these men would take away his title on a good night? Or both?