Is it necessary to make up for days of fasting that included various colored discharges after the cessation of the usual menstrual bleeding, with doubt regarding the attainment of complete purity?

Yellowish or brownish discharge (صفرة وكدرة) is not considered menstruation unless it occurs during the accustomed period or is connected to blood. Accordingly, what you observed of yellowish or brownish discharge (brown streaks) on the tenth and eleventh days after seeing the sign of purity (الطهر) is not considered menstruation, as long as it is outside your accustomed period. Therefore, your fasting on those days is valid, and you are not required to perform ghusl (ritual bath) after the cessation of that yellowish discharge, because it is not considered menstruation.