Have I become pure if I find slight dryness after waking up, and very light yellow drops appeared on the seventh day of my period? And in this case, is the seventh day considered a full day of the period, and what is the ruling on ghusl and prayer thereafter?

A woman should perform ghusl (ritual bath) and pray as soon as she sees purity, whether by dryness (jufūf) or the white discharge (al-qaṣṣah al-bayḍāʾ). Any yellowish or brownish discharge she sees after attaining purity is not considered menstruation. If she is unsure whether what she sees is a yellowish discharge or vaginal secretions before confirming purity, the default assumption is that menstruation persists, and she should act accordingly until she is certain that purity has occurred. Her ghusl is valid.