Answer:
Hello,
What causes bleeing from under the skin is a bruise. You can tell how bad you're bleeding from under your skin by the color of the bruise. If it's black, you know it's bleeding a lot. If it's yellowy-greeny it's not a major bruise.
Bruises can change color. It also depends on how hard you hit yourself. Say, for example, you got hit in the leg with a soccer ball; and the bruise is black the first day, blue the next, and greeny-yellow the next day; you can tell the bruise is starting to stop bleeding too much.
From,
Dr. Serogia