The original question had to be edited.  The most striking social concept that is evident in the narrative is how life changes for Williams when he is socially deemed as "White" and when he is deemed as a person of color.  Williams is still the same person.  Yet, social construction is painfully evident in this realm.  When society perceives him one way, doors open and opportunity becomes evident.  When society perceives him in another, there is a painful reality evident. 

Williams' narrative demonstrates how the social concept of race goes very far to define one's consciousness.  Williams does recognize that he has the power to define his own narrative, so race is not shown to define him entirely.  Yet, the social construct of race that is shown causes reflection in the reader.  The question as to how society constructs the issue of race and the people within it, those who "live on the color line," resonates in the reader's mind.  The social definition in terms of skin color plays a brutal role in the reality of those who "live on the color line."  Williams' narrative goes far in reflecting how this is evident in the course of the novel.