dark brown discharge from vagina

hi

i am on pills since 10 months and every thing is regular since all that period, until only yesterday i started having dark brown discharge from vagina although i have completed my period one week back, and during the last week every thing was clear and no coloration.
so please could you advice what is this dark brown color is and why i am having it.
i am on my pills as per the schedule, and didnt stop it although the coloration is still available yesterday and today.

waiting for your advice please urgently