Do clear, colorless secretions – not accompanied by any discharge and lasting for a day – constitute a valid sign of purity, knowing that they are followed by a small amount of yellowish fluid and then thick white secretions?

If a woman sees purity by one of its two signs, then she has become pure and ghusl becomes obligatory upon her. Normal vaginal discharge has no effect. As soon as purity is seen, ghusl must be performed, and any yellowish or brownish discharge seen after that is not considered menstruation.