I had my periods for 4 days, after 4 days I had a ghusal bath, & kept my fast & read namaz, however just before iftaar I noticed a brownish discharge

The minimum period of Haydh is 3 days and 3 nights and the maximum period is ten days and ten nights. Whatever colour fluid flows in the period of haydh such as red, yellow, green, brown, etc. will all be regarded as haydh until the pad is completely white in colour. When it remains white as it was when placed, the woman will be cleansed from the haydh. However, if she bleeds again before remaining pure for less than 15 days, then the minimum period of haydh is 3 days and 3 nights and the maximum period is ten days and 10 nights. Whatever fluid flows within 10 days, it will be regarded as haydh and therefore the fast must be repeated.

and Allah Ta'ala Knows Best

Mufti Ebrahim Desai