The following are Torah true explanations to the verse under discussion since Sunday. Please choose the one you think best captures the author's (ie God's) intention:
1) Rashi: Cushite is code for gorgeous. When the verse says "Isha Cushite" it means the very beautiful Tziporah. Though the same author (ie: God) has previously used the word beautiful (or a synonym) to describe, Sarah, Rivka, Rachel and Joseph, here he elects to employ a euphemism instead. An explanation for the sudden use of euphemism is not immediately obvious.
2) Ibn Ezra: Cushite is slang for ugly. The verse is speaking of Tsiporah, who was black, and therefore ugly (according to the sensibilities of Ibn Ezra, anyway) The Ibn Ezra does not tell us why the author (ie: God) chose to describe Tsiporah this way, nor does he tell us why the author (ie: God) used a colloquialism here, instead of speaking plainly and directly.
3) Rashbam: The pshat (Rashbam's word, not mine) is that Moshe took an Ethiopian wife.
My vote: (3)
My reason: I prefer to think of God as a straightforward sort of guy. When He says Cushite, I assume he means Cushite. I don't expect Him to use slang, or to suddenly, this deep in the book, become cautious about using the word "beautiful" to describe a pretty girl. (Rashbam's pshat is also supported by the legend retold by Josephus, and the Sefer Hayashar.)
Please vote in the comments.
(PS: Sincere apologies to anyone offended by the title of my previous post. I should have been more careful.)