TT #63 · Parshas Tazria · Aliyah 1 · Passuk 2
English: When a person has on the skin of the body a swelling, a rash, or a discoloration, and it develops into a scaly affection on the skin of the body, it shall be reported to Aaron the priest or to one of his sons, the priests.
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:2
Torah Temimah cites Mishnah Negaim 1:1 for the Sages’ definition of the appearance called se’eis.
English: The Sages say: se'eis is like white wool, and the shade below it is like the membrane of an egg.
Definition
The Mishnah identifies the appearance called se'eis as white wool; according to the Sages, its secondary shade resembles an eggshell membrane.