What is the ruling regarding menstrual blood that alternates consistently between black and red for fifteen days each month?

Primary text

If a woman observes black blood for fifteen days and red blood for fifteen days each month, the entirety of the black blood is considered menstruation (Hayd). This is because the black blood is fit to be menstruation, and its appearance is an indication of menstruation, thus establishing it as such. Consequently, she must abstain from prayer during these days, and perform Ghusl (ritual bath) immediately upon their completion.