Another thing to remember is that Leroi Jones/Baraka is calling for something of a revolution in this play.  He is showing us that Clay's attempt to be "white" is futile and that he will never be received into "white" society.  It is a dark view of the dominant culture and how that culture represses minorities in particular African Americans.  The play also features a group of co-conspirators who can't be ignored.  They are essential to the play's meaning in that they help push Clay's body off the train.  This is quite an indictment of white society.   And finally, neither of the two characters are what they appear to be.  Clay cannot hide his "blackness" and ultimately his anger no matter what he does.  Sadly, Lula knows how to exploit his weakness and uses her sexuality to manipulate and expose Clay's hidden hatred.   These are complex and disturbing characters to say the least.

The conflict in this wonderful play by Amiri Baraka is clearly the conflict between Lula and Clay, beginning with her seducing him, her racist comments, and clearly coming to a climax with the stabbing, and ultimate death of Clay.  The racial tension is fraught throughout the play.  Clay and Lulu are the only real characters in the play (the others on the subway play a minimal role), therefore the characterisation that you're looking for much be of them:

Clay is a typical bourgeois black male, so predictably bourgeois that Lula is able to tell his life history by the evidence of his dress (a too-narrow suit coat), his demeanor (decorous, tentative), and his style of speech (middle class, intellectual, full of pretensions). 

The Caucasian Lula is a thirty-year-old femme fatale who alternately seduces and insults Clay. She is a mythical apple-offering Eve to his clumsy and naive Adam. Lula is the embodiment of Western Civilization, seductive and ferociously greedy, relentless, but also psychotic, lonely, trapped by her own cultural identity.