Why does a woman's menstrual blood turn black?

　　Menstruation is due to Uterus The endometrium sloughs off periodically with bleeding, about once a month. The first menstrual period is called menarche. Menstrual blood is alkaline, dark red in color, odorless, thick and not coagulated. In addition to blood components, menstrual blood also contains fragments of endometrium, cervical mucus, etc.

　　What should I do if my menstrual blood turns black?

　　When I started menstruating when I was 16 years old, my menstrual flow was smaller than others, and it usually cleared up in 3 days. I don’t know if this is normal. And when I came there, the color was a bit dark and it looked quite disgusting. What's going on?