Firtsly I should state that not all policies and laws must come directly form the Bible. Secondly, on the topic of miscegenation, there are a few quotes from the Bible implying it is negative or even sinful. Even barring these, however, God put different races on Earth (or indirectly allows them to evolve from humans who were scattered across the planet), so wiping one out (with the obvious exception of the Jews) through such naturally adverse means would be illogical and bad for everyone involved.

As for the question of an athesit White vs a Christian black, I would distrust both naturally. Atheist Whites have a historical tendency to fall to and promote liberalism, race mixing, communism, and democracy. Blacks, obviously have a biological tendency towards crime and lower IQ. Neither are good to associate with too much, however the Black would undoubtedly cause more abrasion with differences of culture, understanding, etc., making him more difficult to work with.