|Was it the color of his wife's skin that so disturbed Moses' sister?|
Let's take a look at what the Bible actually says (Numbers 12):
Clearly, Miriam says something negative about Moses, questioning why he should be put on a pedestal. She is stricken by leprosy, and only healed after Moses prays for her (v. 13). The only tricky part of the story is understanding what Miriam's criticism of Moses actually was. All it says is, He married a Cushite woman. What was wrong with that?
One idea is that Moses' wife was black, but the word for that is , and besides why would her skin color be such a big deal? Another idea is that Moses separated from his wife, but this is not implied anywhere in the verse.
The correct interpretation hit me years later. It wasn't that Miriam was Cushite per se - it's that she wasn't Israelite. Moses had married a non-Jew. To Miriam, this was a problem.
God's response towards Miriam is swift and rather unforgiving. If not for Moses' intervention, Miriam would likely have died from the illness. This should be a lesson to Jews who lament and disparage intermarriage. Intermarriage between Jews and non-Jews is nowhere forbidden in the Hebrew Bible, except with very specific nations. Being obnoxious, however, can put you in danger - particularly if you are assaulting someone close to God.