Albert Barnes Commentary Leviticus 13:31

"And if the priest look on the plague of the scall, and, behold, the appearance thereof be not deeper than the skin, and there be no black hair in it, then the priest shall shut up [him that hath] the plague of the scall seven days:" — Leviticus 13:31 (ASV)

There is no black hair in it; more probably, there is no yellow hair in it.