Was what you did, in completing the fast and the prayer, correct, knowing that you saw a brownish discharge (which you considered to be blood) while using the restroom after performing ghusl from menstruation and praying Fajr, and then saw blood after Ishā' prayer? And must you make up the Dhuhr, Asr, and Maghrib prayers if we assume that what descended at noon was blood?

If a woman has verified her state of purity (tahara), and then doubts whether bleeding has recurred or not, the default assumption is that it has not recurred. Any discharge she saw that was brownish (kudrah) is considered valid, and fasting on that day is valid and does not require قضائها (making it up), nor do the prayers. However, if bleeding recurs, she is considered to be menstruating again (ha'idh) and must perform ghusl (ritual bath) after it stops. The period of purity (tuhr) that occurred during her menstruation, during which she fasted, is a valid purity, and she is not required to make up that day.