When is a woman considered to be menstruating and should cease praying if a small amount of reddish discharge appears for one day, followed by a brownish discharge for five days, then bright red blood for six or seven days?

As long as the bleeding does not exceed fifteen days, all of it is menstruation, whether it is characterized by redness or by brownish discharge, because yellowish and brownish discharges during the days of menstruation are considered menstruation.