The hefsek taharah does not have to be totally clear. However, it does have to show that uterine bleeding has stopped. A brown color on the hefsek taharah, unless it is a light beige or tan with no hint of red, needs to be evaluated by a halachic authority. Your patterns from previous months and lack of subsequent staining do not, in and of themselves, change the status of the bedikah.

Unfortunately, in a case like this, when you are uncertain of the color and the cloth is no longer available, it cannot be relied on as a hefsek taharah. You can retroactively count a bedikah from the following day as a new hefsek taharah. Your clean days and immersion are pushed off by one day.

In the future, we recommend saving any questionable bedikot in a clean place until you are certain whether you wish to consult about the color.