What is the ruling on fasting the day after performing ghusl following menstruation if blood reappears after breaking the fast?

Your fast is valid as long as you saw the blood after sunset, and you are not required to make up for it. The purity interspersed within the menstrual period is a valid purity, so there is no need to make up for any obligatory acts of worship performed during it. As for the returning blood, it is considered menstruation unless the total days of bleeding and the interspersed clean days exceed fifteen days.