Must one make up for the days accompanied by brownish discharge, given that red blood did not appear until later?

Your fast is valid and you are not required to repeat it, as long as you saw the brownish discharge outside the time of your regular period. It is considered menstruation if you see blood followed by yellowish or brownish discharge, and the total duration reaches a day and a night. In this case, you are required to make up the fast of those days.