Vayikra 13:3

הפך לבן [THE HAIR …] IS TURNED WHITE — This means that at first it was dark, and it turned white within the plague. The smallest number of hairs implied by the term שער is two (Sifra, Tazria Parashat Nega'im, Chapter 2 2). עמק מעור בשרו [THE PLAGUE] IS DEEPER THAN THE SKIN OF HIS FLESH — Every white colour is deep (in contrast to a dark colour surrounding it) just as the colour of anything illuminated by the sun is deeper than the shadow (Shevuot 6b). וטמא אתו HE SHALL PRONOUNCE HIM UNCLEAN — He (the priest) shall say to him. “Thou art unclean” — for it is an enactment of Scripture that hair that has become white is a symptom of uncleanness.

and the priest shall look on the plague in the skin of the flesh: and when the hair in the plague is turned white, and the plague be deeper in appearance than the skin of his flesh, it is a plague of żara῾at: and the priest shall look on him, and pronounce him unclean.

וְרָאָ֣ה הַכֹּהֵ֣ן אֶת־הַנֶּ֣גַע בְּעֽוֹר־הַ֠בָּשָׂ֠ר וְשֵׂעָ֨ר בַּנֶּ֜גַע הָפַ֣ךְ ׀ לָבָ֗ן וּמַרְאֵ֤ה הַנֶּ֙גַע֙ עָמֹק֙ מֵע֣וֹר בְּשָׂר֔וֹ נֶ֥גַע צָרַ֖עַת ה֑וּא וְרָאָ֥הוּ הַכֹּהֵ֖ן וְטִמֵּ֥א אֹתֽוֹ׃