When should one stop praying and fasting if the color of the discharge changes a day or two before menstruation, without any blood appearing afterward?

Scholars have differed concerning yellow and turbid discharge before menstruation. The more preponderant opinion is that it is considered menstruation if it occurs within the customary period, but not if it occurs outside of it. So, if a woman sees it during her customary days, she refrains from prayer and fasting. But if it occurs outside her customary days, she prays and fasts, and is considered pure.