Legend says that a blue eyed man came from the sky and then the mother of the Chengizhan was pregnant. Some people say this man might be Qirghiz. Among Chengizhans sons only Qubiley had black hair, then Chengizhan commented that "Qubiley looked like his uncles". That means Chengizhan didn't look like his brothers.
That doesn't matter actually. Chengizhan was Mongol, he was raised in Mongol society, and united the Mongol tribes and became the leader of the Mongols, and created a new history for the Mongols.