Is light blood that appears after intercourse in the last days of menstruation or a day after it considered menstruation, and is ghusl (ritual bath) obligatory for it?

The blood that returns on the fifth day is considered menstrual blood, because it falls within the period of menstruation. If this blood stops, you must perform ghusl again. If you are in a state of janabah, you should perform ghusl with the intention of purifying from both janabah and menstruation to remove both impurities. There is no objection for your husband to have intercourse with you once you see purity and have performed ghusl from menstruation. During this period of purity, you are obligated to observe what is incumbent upon women who are pure, such as prayer and the like. The purity that intervenes during menstruation is considered a valid state of purity.