From TCM's Movie Morlock's blog (a site I highly recommend to all you classic movie geeks):
It is brownface, and in the case of Rita Moreno, who is Puerto Rican, quite literally so. She had dark make-up put on her, as did George Chakiris, and all the others, with the same shade of brown to make them look the same – except for Natalie Wood. She wasn’t in brownface, although it is “brownface” in the sense that she’s someone of Eastern European descent, a known white actress here playing a different ethnicity, a New York Puerto Rican; a New Yorican. Is that a problem? Only in the theoretical sense that there may have been other actors they could have gone to. But not really… because in Hollywood at that time the only Puerto Rican actors we knew from going to the movies were José Ferrer and Rita Moreno. But even though Moreno had been doing her thing in MGM since the mid-50′s she wasn’t a big movie star. Natalie Wood was hired to “play” a Puerto Rican, to act; and acting is what actors do.
Words from film scholar Ernesto Acevedo-Muñoz (who's also Puerto Rican) on West Side Story, which will be screened in select theaters nation-wide on November 9th, to celebrate the film’s 50th Anniversary. As TCM notes, the film marked the first time Puerto Ricans were the focus of a mainstream film production.
Mr Acevedo-Muñoz is currently penning a book on the film which will defend its representation of Puerto Ricans, as he begins above. Read the rest of the Movie Morlock's piece HERE.