Who was the Kushite woman? And how did she turn black?

Towards the end of parshas Behaalosecha, in the 12th perek:

א וַתְּדַבֵּר מִרְיָם וְאַהֲרֹן בְּמֹשֶׁה, עַל-אֹדוֹת הָאִשָּׁה הַכֻּשִׁית אֲשֶׁר לָקָח: כִּי-אִשָּׁה כֻשִׁית, לָקָח.

1 And Miriam and Aaron spoke against Moses because of the Cushite woman whom he had married; for he had married a Cushite woman.

Ibn Ezra writes on that pasuk a bunch of explanations, all fascinating, but he ends with his own position:

והישר בעיני שזו הכושית היא צפורה, כי היא מדיינית ומדיינים הם ישמעאלים והם דרים באהלים.
וכן כתוב: ירגזון יריעות ארץ מדין ובעבור חום השמש אין להם לבן כלל, וצפורה היתה שחורה ודומה לכושית.

וטעם כי אשה כשית לקח –
זה הדבור שדברה מרים.
ומה נכבד דברי קדמונינו שאמרו על הזקנים:

אשריהם ואוי לנשיהם.

והנה חשדו משה כי לא נמנע לשכב עם צפורה, רק בעבור שאיננה יפה.

That is, they were not complaining that he had married the Kushite woman, but about his conduct towards the Kushite woman. And this Kushite woman was Tzipporah, and Moshe had separated from her. (Thus Ibn Ezra manages to get lakach to mean garash in effect, even though he does not translate it this way.) Thus, woe to the wives of the elders. They suspected that Moshe was only separating from Tzipporah because she was not beautiful. (And with that he goes against the explanation of Kushit as beautiful.)

I disagree with this explanation, and specifically with his identification of Tzipporah with the Kushite woman. This is a nice midrashic closed-canon approach, but on a peshat level, no way. The whole parenthetical remark at the end of the pasuk of ki isha kushit lakach is to tell us something we did not know. They were speaking about the Kushite woman. Oh, by the way, he had married a Kushite woman. Compare to the parenthetical note by Yonah. And surely the reader knows of Tzipporah's existence!

So I don't agree with Ibn Ezra. But I am more interested in his explanation of why she was a Kushite woman. Ibn Ezra wrote:

והישר בעיני שזו הכושית היא צפורה, כי היא מדיינית ומדיינים הם ישמעאלים והם דרים באהלים.
וכן כתוב: ירגזון יריעות ארץ מדין ובעבור חום השמש אין להם לבן כלל, וצפורה היתה שחורה ודומה לכושית

"And what is correct in my eyes is that this Kushite woman is Tzipporah, for she was a Midianite woman, and the Midianites are Ishmaelites, and they dwell in tents. And so it is written {Chabakuk 3:7}:

ז תַּחַת אָוֶן, רָאִיתִי אָהֳלֵי כוּשָׁן; יִרְגְּזוּן, יְרִיעוֹת אֶרֶץ מִדְיָן.

7 I see the tents of Cushan in affliction; the curtains of the land of Midian do tremble.

{And though Ibn Ezra does not mention it explicitly, note the juxtaposition which he surely intends in part.}

And because of the heat of the sun, they have no whiteness at all, and Tzipporah was black and similar to a Kushite woman."

Now, the sun can tan people to a great degree, but to turn them black? Well, Pliny ascribed an Ethopian's black skin to sunburn. "Galen, in his Temperament. 2.616, attributes the woolly hair of the Ethiopians to the effect of heat." And to cite Strabo, the Greek geographer:

Now in this he is correct; but no longer so when he lays the black complexion and woolly hair of the Aethiopians on merely the waters and censures Theodectes,27 who refers the cause to the sun itself, saying as follows: "Nearing the borders of these people the Sun, driving his chariot, discoloured the bodies of men with a murky dark bloom, and curled their hair, fusing it by unincreasable forms of fire." But Onesicritus might have some argument on his side; for he says that, in the first place, the sun is no nearer the Aethiopians than to any other people, but is more nearly in a perpendicular line with reference to them and on this account scorches more, and therefore it is incorrect to say, "Nearing the borders . . . the sun," since the sun is equidistant from all peoples; and that, secondly, the heat is not the cause of such a discolouration, for it does not apply to infants in the womb either, since the rays of the sun do not touch them. But better is the opinion of those who lay the cause to the sun and its scorching, which causes a very great deficiency of moisture on the surface of the skin. And I assert that it is in accordance with this fact that the Indians do not have woolly hair, and also that their skin is not so unmercifully scorched, I mean the fact that they share in an atmosphere that is humid. And already in the womb children, by seminal impartation, become like their parents in colour; for congenital affections and other similarities are also thus explained. Further, the statement28 that the sun is equidistant from all peoples is made in accordance with observation, not reason; and, in accordance with observations that are not casual, but in accordance with the observation, as I put it, that the earth is no larger than a point as compared with the sun's globe; since in accordance with the kind of observation whereby we feel differences in heat — more heat when the heat is near us and less when it is far away — the sun is not equidistant from all; and it is in this sense that the sun is spoken of29 as "nearing the borders" of the Aethiopians, not in the sense Onesicritus thinks.

Thus, there are competing theories, and Ibn Ezra combined into this that they typically live in tents (rather than being close to the sun) and thus are exposed to the elements. He does not seem to consider genetics to play a factor, as far as I can tell, except of course that such traits can be passed down.

I would end with a reference to Shir Hashirim, where tents are mentioned, and how the heroine is black (or extremely tan) as a result of exposure to the sun:

ה שְׁחוֹרָה אֲנִי וְנָאוָה, בְּנוֹת יְרוּשָׁלִָם; כְּאָהֳלֵי קֵדָר, כִּירִיעוֹת שְׁלֹמֹה.	5 'I am black, but comely, O ye daughters of Jerusalem, as the tents of Kedar, as the curtains of Solomon.
ו אַל-תִּרְאוּנִי שֶׁאֲנִי שְׁחַרְחֹרֶת, שֶׁשְּׁזָפַתְנִי הַשָּׁמֶשׁ; בְּנֵי אִמִּי נִחֲרוּ-בִי, שָׂמֻנִי נֹטֵרָה אֶת-הַכְּרָמִים--כַּרְמִי שֶׁלִּי, לֹא נָטָרְתִּי.	6 Look not upon me, that I am swarthy, that the sun hath tanned me; my mother's sons were incensed against me, they made me keeper of the vineyards; but mine own vineyard have I not kept.'