TT #99 · Parshas Tazria · Aliyah 2 · Passuk 6
English: And the kohen shall see him on the seventh day a second time. And, behold! the lesion has become dimmer, and the lesion has not spread on the skin, the kohen shall pronounce him clean. It is a mispachath. He shall immerse his garments and become clean.
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:6
Torah Temimah cites Sifra (Toras Kohanim) for the continuing classification of the lesion despite a change in appearance.
Sifra — Vayikra 13, Midrash Sefer
English: Even though its appearance has changed, it remains a mispachath.
Textual derivation
A change in shade does not by itself remove the lesion from the classification of mispachath.