It is interesting that race plays a key role in the way that Iago works against Othello. Note the rather grim visual images Iago shouts out to Brabantio about a black ram tupping his white daughter. Whatever status and nobility Othello has managed to win for himself, it is clear that issues of race are still of vital importance, and this is one of the ways that Iago works against his master.
I think that race is a part of the larger dynamic of "insider" vs. "outsider" that Othello of which Othello is both part and victim. The fundamental notion of being an "outsider" is something that is a part of Othello's narrative. The soldier/ warrior made into a man of title, the fact that his background is not the same as others in Venetian society, and the fact that he is a man of color all represent obstacles that traditionally relegate voices to the periphery. Yet, Othello's difference is that he has been brought into the center of this dynamic. He is awarded title, and has Desdemona as his love. These are traits that reflect a status of being "inside." Yet, through his own insecurity about this position, race becomes one of the primary wedges that divide Othello from his own sense of self. The racism upon which Iago preys and the attitudes that are latent in Venetian society are both elements that cause Othello to enter the realms of doubt and insecurity about his very state of being. I don't think that racism is the only element at play here, as Iago is extremely smart in plotting his manipulation into multiple and different realms, in which race is one part.