Why does the priest not need to look for yellow hair, if the infection does spread after the person's cleansing?
If the infection spread after the person has been declared clean, the priest must examine him once again. If the infection has indeed spread, the person is declared unclean. There is no need for the priest to look for yellow hair as the symptoms are already clear.
36 then the priest shall examine him, and if the itch has spread in the skin, the priest need not seek for the yellow hair; he is unclean.