What is the ruling on fasting and making up prayers for one who saw light, pinkish-brown blood two minutes before Maghrib Adhan while making up for Ramadan, then it became only brown threads on the following days?

The questioner's cessation from prayer is an error. The ruling issued is that the minimum duration for menstruation is one day and one night. If the total duration of what she saw did not reach this period, then it is not considered menstruation. Her fast is valid, and she is not required to perform ghusl. She must make up the prayers she missed.