Is what the questioner is doing correct, and are the colors she described over ten days considered menstruation? And is she sinful for following a specific fatwa concerning how to deal with the yellow and brown discharges she sees before and after menstruation, to the exclusion of others?

Yellowish or brownish discharge is considered menstruation if a woman sees it after the minimum period of purity between two menstruations has passed. This is the view of the majority of scholars. She must stop praying as soon as she sees it, even before any blood appears. A woman does not become pure until the bleeding stops, along with any subsequent yellowish or brownish discharge, as long as it is within the possible duration (fifteen days). If that stops and she sees the white discharge (al-qassah al-bayda') or dryness, then she performs ghusl.