Nothing at all. Moses married a black woman and he knew Gods law better than anyone else.
Num 12:1 And Miriam and Aaron spake against Moses because of the Ethiopian woman whom he had married: for he had married an Ethiopian woman.
Scripture DOES prohibit believers marrying unbelievers though
2Cr 6:14 Be ye not unequally yoked together with unbelievers: for what fellowship hath righteousness with unrighteousness? and what communion hath light with darkness?
2Cr 6:15 And what concord hath Christ with Belial? or what part hath he that believeth with an infidel?
2Cr 6:16 And what agreement hath the temple of God with idols? for ye are the temple of the living God; as God hath said, I will dwell in them, and walk in [them]; and I will be their God, and they shall be my people.
2Cr 6:17 Wherefore come out from among them, and be ye separate, saith the Lord, and touch not the unclean [thing]; and I will receive you,
2Cr 6:18 And will be a Father unto you, and ye shall be my sons and daughters, saith the Lord Almighty.