Niddah 2:5-6

Niddah 2:5

The Sages described the uterus as a room with an antechamber and a loft. Blood in the room is ritually unclean. In the antechamber (where it could have come from either the room or the loft), the case of doubt is ruled unclean because of the presumption that it came from the uterus.

Niddah 2:6

Five colors of a woman’s blood are ritually unclean: red, black, the color of crocus leaves, the color of water mixed with earth, and the color of diluted wine. Beis Shammai add the color of water in which fenugreek was soaked and the color of the juice from roasted meat but Beis Hillel rule these clean. Rabbi Akavya ben Mehalalel ruled yellow ritually unclean but the Sages ruled it clean. Rabbi Meir said that yellow doesn’t convey impurity as a stain but it does convey impurity as a liquid; Rabbi Yosi says that it doesn’t convey impurity in either state.