Bruising is another common sign of a broken ankle.
Bruising or discoloration is from blood. Usually, blood is contained in the blood vessels (arteries and veins). After an injury, blood leaks out of the blood vessels and pools in the flesh and muscle, where you can see it.
There’s one more sign commonly associated with broken bones: crepitus. This one is harder to imagine. It can’t be seen, but it can be felt. It’s the broken bits of bone grinding on each other with movement or manipulation of the injury. To the person feeling for it, it can be described as a bag of gravel. Not fun.