Is ghusl obligatory after seeing yellow discharge following the cessation of menstrual bleeding, given that there was a previous white discharge, and is it permissible to intentionally expel discharge to verify purity?

Do not pay attention to whispers [waswas]. A woman knows purity by one of two signs: she inserts a piece of cotton into the private part, and if she finds it free of blood, yellowness (صفرة), and brownish discharge (كدرة), then she has become pure, and it is obligatory for her to perform ghusl (ritual bath). As for any yellowness or brownish discharge a woman sees after that, it is not to be given attention to, because it is not connected to blood. It is obligatory for a woman to place the cotton on the outer part of the vulva, then look; if it is free of blood, yellowness, or brownish discharge, then she has become pure.