Fiqh-us-Sunnah Volume 1, Purification and Prayer, Fiqh 1.069A.

1. Dark. Once, when Fatimah bint Abu Habash had a prolonged flow of blood, the Prophet told her, “If it is the blood of menstruation, it will be dark and recognizable. If it is that, then leave the prayer. If it is other than that, then make ablution and pray, for it is only due to a vein.” This is related by Abu Dawud, an-Nasa’i, Ibn Hibban and ad-Daraqutni, who said all of its narrators are trustworthy. Al-Hakim also related it, and said that it meets Muslim’s standards.

2. Red. It is the original colour of blood.

3. Yellow. It is a liquid, like pus.

4. A muddy colour. It is an intermediate colour between black and white, like dirt.

Malik and Muhammad al-Hassan (and al-Bukhari in mu’allaq form) recorded that women would send ‘Aishah small boxes with yellow-stained cotton, and she would tell them, “Do not be in haste until you see the pure white cotton.” If the discharge is yellow or muddy during the days of menstruation, it is to be considered as part of the menses. During other days, it is not regarded as such. Umm ‘Atiyyah said, “After we were pure, we did not consider the yellow or muddy discharge to be anything.” This is related by Abu Dawud and al-Bukhari, but without the words “…after we were pure…”