The GOP does not support affirmative action. They believe a man should be judged by the content of his character not the color of his skin.
The democrats support affirmative action where a man is judged by the color of his skin above the content of his character. Therefore if two applicants are trying to get a job or get admitted to a University, AA gives preferential treatment to the minority.
Therefore it is only logical that minorities support the party that supports affirmative action.
Minorities typically vote with the democrats and big "take care of me" government. Are there any minority democrats running congress? Bush had a whole host of republican minorities in his admin.