What is to be done if there is the appearance of blood after a woman is clean from menstrual bleeding, and straight after she has taken a bath?
Answer: If there is some yellowish or muddy discharge after she has become pure from her menstruation, then it does not affect her purity from the menstruation, i.e. she is still pure. The ruling of this discharge is like urine (it should be cleaned).
If however, the discharge is clearly menstrual blood, then she returns to being in a state of menses. So when she becomes clean again (which could be a short time later), she must take a bath (ghusl). This is due to what is established from the Companion, Umm ‘Atiyyah (may Allah be pleased with her) who said: “We did not consider the yellowish and muddy discharge after becoming pure from menses to be of any consequence.”
See Al-Jāmi’ fī Fiqhil-‘Allāmah Ibn Bāz (p. 99).