What is the ruling on delaying the ghusl (ritual bath) from menstruation when in doubt about its cessation, and not seeing signs of purity, with the continuous presence of discharge?

If yellowness or a brownish discharge is connected to menstruation, then it is considered menstruation. If you see dryness or normal white discharge after menstruation, then you must perform ghusl, and pay no attention to any yellowness or brownish discharge you may see after that. If you doubt the cessation of menstruation, the default is that it continues until you are certain otherwise. There is no sin upon you for not praying as long as the total days of menstruation and whatever yellowness or brownish discharge is connected to it do not exceed fifteen days.