how will a blind man define the color black...?

Well... If the person has been blind of of their life then I would suppose that they wouldn't know the definition. Since color is mainly of those who have sight. A person that wasn't born blind remembers it as a color that had no lightness. All in all, born blind or originally sighted..someone who is not blind has no idea how it is to be...

May be as something very luminous, bright, dazzling, hopeful and all that negates darkness to a normal person.