Why Zipporah Was Called the Cushite Woman in Midrash Aggadah

"And Miriam and Aaron spoke against Moses" (Numbers 12:1). At the time when those seventy [elders] were prophesying, the people were saying, "Happy are the mothers of these men, who see their sons as prophets." Zipporah was there, and she began to answer them, "Happy are their mothers, but woe to their wives." Miriam was there, and she said to Zipporah, "And why do you speak this way?" Zipporah said to her, "Because, ever since your brother Moses received the Torah and was bound to [prophetic] speech, he has separated from me." At once Miriam told Aaron, and the two of them began to speak against Moses. About what did they speak against him? Concerning the Cushite woman — that he had acted improperly, in that he had taken a Cushite woman and distanced her. "The Cushite woman" — this is Zipporah. But was she a Cushite? Was she not a Midianite? And why is she called "Cushite"? To tell you: just as this Cushite woman is distinguished in her skin, so was Zipporah the righteous distinguished in her good deeds and in her beauty above all other women. And why does the verse repeat "for he had taken a Cushite woman"? Because, had our teacher Moses sought to find a woman as beautiful in her deeds and in her beauty [as she], he would not have found one.