They're all Caucasian. If there were I hope someone points them out to me. I'm not certain. I can only hypothesize that George Lucas didn't want to risk it. That is to say, he didn't want controversy to develop.
Controversy is often detrimental to someone's image and career, especially film makers.
Lucas had a lot at stake when he released Star Wars. Or, perhaps it never occurred to him to include a rainbow of colors in his cast. Star Wars was written during the late sixties, early seventies, if I'm not mistaken. Racial equality and equality among the sexes were just starting to emerge. Please don't think that I'm calling Lucas racist or sexist.