The normal color of menstrual blood is usually dark red. Depending on the amount of menstrual flow, menstrual blood may also be bright red or light red in color. Menstrual blood is dark red in color and consists mainly of blood, endometrial debris, cervical mucus and shed vaginal epithelial cells. Menstrual blood is usually non-clotting, and clots may appear when the bleeding is heavy or fast. The menstrual period usually lasts from 2 to 8 days, with an average of 4 to 6 days. In the premenstrual period, the bleeding is heavy and the menstrual blood may be bright red; in the late menstrual period, the bleeding gradually decreases and the menstrual blood may be light red. If the color of menstrual blood is dark or light, it is usually abnormal. When the color of menstrual blood is dark and black, it may be old bleeding, mostly due to abnormal development of the cervix and uterus, and the menstrual blood cannot be discharged in time. When the color of menstrual blood is light and pinkish, it often indicates endometriosis, such as endometritis. When the color of menstrual blood is abnormal in the clinic, you should go to the hospital in time to find out the cause and carry out targeted treatment under the guidance of the doctor.