The play is not very much concerned with racial difference; indeed, the protagonist's specific race is not clearly indicated by Shakespeare. Othello is referred to as a "Moor", but for Elizabethan English people, this term could refer either to the Berbers (or Arabs) of North Africa, or to the people now called "black" (that is, people of sub-Saharan African descent), or to Muslims in general. In his other plays, Shakespeare had previously depicted both a Berber Moor (in The Merchant of Venice) and a black Moor (in Titus Andronicus). In Othello, however, the references to the character's physical features do not settle the question of which race Shakespeare envisioned.
In his Arden edition of the play, E.A.J. Honigmann summarises the contradictory evidence. The various uses of the word 'black' (for example, "Haply for I am black") do not help, since 'black' could simply mean 'swarthy' for Elizabethans. Iago twice uses the word 'Barbary' or 'Barbarian' to refer to Othello, apparently referring to the Barbary coast inhabited by the "white" Moors. Yet Roderigo also calls him 'the thicklips', which seems to refer to (perhaps) African physiognomy. Honigmann notes that since these comments are all insults, they need not be taken literally.
Honigmann also notes one piece of external evidence: an ambassador of the Arab King of Barbary with his retinue stayed in London in 1600 for several months and occasioned much discussion. Honigmann wonders whether Shakespeare's play, written only a year or two afterwards, might have been inspired by the ambassador. Also, it should be noted that a real Othello might be a Berber or Arab (northern-African) rather than of entirely sub-Saharan African ancestry. On the other hand, sub-Saharans had visited the Mediterranean long before the time in which the events of the play are set, and a portrayal of Othello as sub-Saharan adds much to the feelings of alienation and suspicion that the audience must sense from him -- here is truly a stranger in a strange land, which makes his psychological plight all the more striking and his final inability to trust his wife the more explicable if he is constantly reminded of the fact that the two of them are from what would then be considered almost literally two different worlds. A Barbary Arab would probably not experience the same emotions; he might not be trusted but he would not be considered totally alien by the Venetians. Therefore when a Barbary Othello cannot trust Desdemona, the audience would be more likely to blame him and not pity him.
Also, interpretations of Othello's origins as "black" were current as of the 1930s, when a performance of the play was banned in a southern U.S. state due to the prejudices against representing an idealized, inter-racial love. The performance included a middle-age African-American performer.
Social predispositions and/or prejudice among modern-day, typical readers and theatre directors lean towards the "black" interpretation, and "white" Othellos have been rare. One exception is Patrick Stewart, who had wanted to play the title role since the age of 14, so he (along with director Jude Kelly) inverted the play so Othello became a white man in a black society.