Otdfbt

צָרַעַת, traditionally translated as leprosy, (perhaps skin disease is more accurate) is compared to snow in three locations:

Exodus 4:6 (ESV) 6 Again, the Lord said to him, "Put your hand inside
your cloak." And he put his hand inside his cloak, and when he took it
out, behold, his hand was leprous like snow.

Numbers 12:10 (ESV) 10 When the cloud removed from over the tent,
behold, Miriam was leprous, like snow. And Aaron turned toward Miriam,
and behold, she was leprous.

2 Kings 5:27 (ESV) 27 Therefore the leprosy of Naaman shall cling to
you and to your descendants forever." So he went out from his presence
a leper, like snow.

Some versions, such as the NIV, translate “white as snow” although the Hebrew lacks the word “white”.

Regarding this comparison, the IVP Bible Background Commentary Old Testament on 2 Kings 5:27 states:

Comparison to "snow" most likely concerns the flakiness rather than
the color.

How is leprosy like snow? Its color, its flakiness, or both? And what is the evidence for making such a claim that it only refers to its flakiness?

According to the first Mishna in Nega'im, the brightest color of Tzara'ath is the white of snow.

מַרְאוֹת נְגָעִים שְׁנַיִם שֶׁהֵן אַרְבָּעָה. בַּהֶרֶת עַזָּה כַשֶּׁלֶג, שְׁנִיָּה לָהּ כְּסִיד הַהֵיכָל. וְהַשְּׂאֵת כִּקְרוּם בֵּיצָה, שְׁנִיָּה לָהּ כְּצֶמֶר לָבָן, דִּבְרֵי רַבִּי מֵאִיר. וַחֲכָמִים אוֹמְרִים, הַשְּׂאֵת כְּצֶמֶר לָבָן, שְׁנִיָּה לָהּ כִּקְרוּם בֵּיצָה:

The appearances of Negaim [diseased patches on skin, clothes, or houses that create impurity] are two which are four: Baheret is bright [white] like snow, its subsidiary is like the lime of the Temple. Se'et is like the membrane of an egg, its subsidiary is like white wool; the words of Rabbi Meir. The Sages say, Se'et is like white wool, its subsidiary is like the membrane of an egg.

When talking about snow, in regards to Tzara'ath, it refers to the whiteness of snow; snow being the whitest white known at the time.

As the Bartenarua there says:

בהרת עזה כשלג. לבנה ביותר. דכתיב (ויקרא י״ג) ואם בהרת לבנה היא, היא לבנה ואין למעלה ממנה לבנה:‏

Back to your quotes:

• Exodus 4:6 the Targum translates it as וְהָא יְדֵהּ חַוְרָא כְתַלְגָא - and his hand was white as snow. Rashi concurs saying דֶּרֶךְ צָרַעַת לִהְיוֹת לְבָנָה – "וְאִם בַּהֶרֶת לְבָנָה הִיא" - the nature of Tzara'ath is to be white.


• Numbers 12:10 once again the Targum says וְהָא מִרְיָם חַוְרָא כְּתַלְגָא - and behold Miriam was white like snow.


• 2 Kings 5:27 once again the Targum says וּנְפַק מִן קֳדָמוֹהִי חִוָר כְּתַלְגָא - and he walked away from him white like snow.

Actually, nowhere do we find that Tzara'ath is flaky. Au contraire, I suspect that if the skin were to become white and flaky then it may not be considered Tzara'ath; but right now I can't prove it.

While I'm giving Danny the space to still improve his answer, and agree with his position (see Mendelssohn's Biur here for some discussion of this, and see also Targum Shiv'im here as to whether or not they translate and his hand returned to the color of flesh, although you have to know Old Greek), I wanted to see what support I could find to argue the other point, that the snow describes the scaliness. While at first glance it seems hard to find support, I will do my best.

Shemos 4:6-7 is the case we will examine, and you can extrapolate to other cases (I used the JPS translation not because it translates it in this way, but because it was the first translation available):

וַיֹּאמֶר֩ יְהוָ֨ה ל֜וֹ ע֗וֹד הָֽבֵא־נָ֤א יָֽדְךָ֙ בְּחֵיקֶ֔ךָ וַיָּבֵ֥א יָד֖וֹ בְּחֵיק֑וֹ וַיּ֣וֹצִאָ֔הּ וְהִנֵּ֥ה יָד֖וֹ מְצֹרַ֥עַת כַּשָּֽׁלֶג׃

The LORD said to him further, “Put your hand into your bosom.” He put his hand into his bosom; and when he took it out, his hand was encrusted with snowy scales!

Why might a translator choose to focus on scales rather than on the color? Well, if we look at the following passuk, we see that after returning his hand to his bosom, it returned to look like flesh. While this could be interpreted as the color of flesh, it may simply refer to the look of regular flesh (i.e. not scaled):

וַיֹּ֗אמֶר הָשֵׁ֤ב יָֽדְךָ֙ אֶל־חֵיקֶ֔ךָ וַיָּ֥שֶׁב יָד֖וֹ אֶל־חֵיק֑וֹ וַיּֽוֹצִאָהּ֙ מֵֽחֵיק֔וֹ וְהִנֵּה־שָׁ֖בָה כִּבְשָׂרֽוֹ׃

And He said, “Put your hand back into your bosom.”—He put his hand back into his bosom; and when he took it out of his bosom, there it was again like the rest of his body.—

The only support I can bring for this here is the translation of the Peshitta here, and perhaps the others who stay silent on the issue.

The Peshitta translates our passuk as:

והא אידה מגרבא איך תלגא

and his hand was as "garva" as snow

What does garva mean? Garav, as explained by Rashi to Vayikra 21:20, is a type of dried scaly boil. If so, the simplest read of this Passuk would be to say that his hand was as scaly as snow. (Note that we have no indication that Garav was white.)

However, the Peshitta translates all tzara'as as garva, meaning the meaning of tzara'as is scales/scaly.

Therefore, for all those who translate tzara'at here as leprosy or some other scaly disease (as opposed to Onkelos here, who translates tzara'at as white, as opposed to his regular translation of segira), they would also be understanding the passuk to be saying "and his hand was scaled like snow".