How can purity be determined if the fluids after menstruation are pale yellow, and is yellowness after blood considered menstruation or istihadah (non-menstrual bleeding)?

Scholars differed concerning the ruling on yellowish and brownish discharges. The preponderant opinion is that they are considered menses during the customary period. So, if a woman sees purity, then sees yellowish and brownish discharges during her customary period, they are menses. But if she sees them after her customary period, they are not menses, based on the hadith (definition) of Umm Atiyyah (may Allah be pleased with her): "We did not consider yellowish and brownish discharges after purity to be anything." As for white discharge, it is not menses at all; rather, it is a sign of purity.