After Moses fled Egypt, he fled to Midian (Ex 2:15). There, he married Zipporah. The Midianites were likely a semitic people descended from Keturah. However, that is not certain, as Keturah’s heritage or nationality is not identified. Midian was one of her sons that Abraham sent to the east before his death. Evidently, the Midianites and Ishmaelites intermarried to the point where the distinction was small (Ge 37:28).
However, there are some that maintain that Zipporah is the Cushite woman mentioned in Numbers 12 (“Ethiopian woman” in KJV). Given the timing of Numbers 12, right after the appearance of manna in Numbers 11, this is a real possibility. She could have been of darker complexion, and their descendants could have lost some of the darker color through intermarriage with the rest of the Levite tribe. This is similar to Joseph marrying an Egyptian, and the descendants of Joseph today are predominantly lighter skinned in appearance.
Whether Zipporah was a Cushite or Moses married a Cushite later does not change one thing: The Bible does not condemn interracial marriages. It does condemn the Israelites marrying those of the land of Canaan because of their religious practices. However, the story of Rahab points to God’s mercy whenever one repents.
Nothing more is mentioned of the Cushite woman afterwards.
Presumably, Abraham circumcised all of his sons, including Midian. In spite of Zipporah being a descendant of Abraham, it is obvious that she was not in favor of circumcision.
And it came to pass by the way in the inn, that the LORD met him, and sought to kill him.
Then Zipporah took a sharp stone, and cut off the foreskin of her son, and cast it at his feet, and said, Surely a bloody husband art thou to me.
So he let him go: then she said, A bloody husband thou art, because of the circumcision.
~ Ex 4:24-26
Zipporah was the daughter of Reuel/Raguel (“friend of God”) or Jethro (“his abundance”), a priest (Ex 2:17-18; 3:1; Nu 10:29). It was likely that he was not a priest of the true God. It appears that Moab and Midian may have had a shared religion. The story of Balaam of Peor points out there was some type of relationship between the nations. The king of Moab addressed the “elders of Midian” (Nu 22:4). The elders of both Moab and Midian were sent to the prophet (v7). Afterwards, Balaam apparently suggests a way to get Israel to fall into disgrace with God. Notice both Midian and Moab are involved in this incident as well:
And Israel abode in Shittim, and the people began to commit whoredom with the daughters of Moab.
And they called the people unto the sacrifices of their gods: and the people did eat, and bowed down to their gods.
And Israel joined himself unto Baalpeor: and the anger of the LORD was kindled against Israel.
…And, behold, one of the children of Israel came and brought unto his brethren a Midianitish woman in the sight of Moses, and in the sight of all the congregation of the children of Israel, who were weeping before the door of the tabernacle of the congregation.
…Now the name of the Israelite that was slain, even that was slain with the Midianitish woman, was Zimri, the son of Salu, a prince of a chief house among the Simeonites.
And the name of the Midianitish woman that was slain was Cozbi, the daughter of Zur; he was head over a people, and of a chief house in Midian.
~ Nu 25:1-3, 6, 14-15
After the incident of the “bloody husband”, it appears that Moses sent Zipporah and their sons back to Midian while he went on to Egypt (Ex 18:2-5). Jethro brought Zipporah and their sons when he met Moses at Mt Sinai. Since this would have been soon after the manna started falling (Ex 16:15), this lends support to the theory that Zipporah and Moses’ Cushite wife are one and the same. Aaron met Moses on the way to Egypt (Ex 4:14) after the “bloody husband” incident (v27), so if Moses sent Zipporah back to Midian before meeting Aaron, it is likely neither he nor Miriam would have known much, if anything, about Zipporah.