What should a woman do if, during her menstrual period, she sees a very light yellow or brown discharge, or a very small drop of blood, which then stops for a day or more, after which normal blood appears?

What a woman sees at the beginning of her menstrual period is considered menses (hayd), and she must refrain from prayer and other prohibitions associated with menstruation. Yellowish discharge (sufrah) and brownish discharge (kudrah) are considered menses if they occur during the time of menstruation, but not if they occur outside of it.