What is the ruling on purity (taharah) if one sees a yellowish discharge (kudrah) after urinating, despite preceding dryness? And is it obligatory to repeat the prayer if one doubts the purity of the garment before prayer, and then its purity becomes clear after completing it?

Turbidity (dark discharge) is not considered menses unless it occurs during the accustomed period or is connected to blood. If a woman sees dryness, she has become pure thereby and must perform ghusl. Any turbidity after that is not considered menses as long as it is outside the usual time. Nothing is incumbent upon the questioner, and her prayer is valid as long as she does not pay attention to doubt.