What is the ruling on not verifying purity after every prayer on the sixth day of menstruation, due to the assumption that brownish discharge continues and ruling out the appearance of white discharge?

Turbid discharge connected to menstruation is considered part of menses. The sign of purity (ṭahārah) is seeing the white discharge (al-qaṣṣah al-bayḍāʾ) or complete dryness (al-jufūf al-tāmm), and some women only experience dryness. Whoever doubts their purity, the default is that she remains in menstruation, and she is not obligated to make up prayers whose obligation she doubts. A menstruating woman must check for purity at the time of every prayer to avoid missing it.