Is a woman considered ritually pure when clean discharge appears after the brownish discharge (Kudrah) or residual blood in the last days of her menstrual period, with the possibility of that discharge returning?

Purity is achieved either by dryness or by the emission of a white discharge. If you are not certain that either of these has occurred, the default assumption is that menstruation persists. The emission of semen unmixed with any brownish discharge does not necessitate the achievement of purity. Rather, you must verify dryness by inserting a piece of cotton into the outer part of the vulva, and it should emerge clean, without any trace of blood, yellowish discharge, or brownish discharge.