A bruise appears after a blow to the head or trunk, which could indicate internal injury. If you are experiencing specific symptoms,

Immediately after the injury, fresh, oxygen-rich blood appears bright.

(bruises) are common skin discolourations that occur when small blood vessels (capillaries) near the skin's surface break from the impact of an injury, causing blood to leak into the surrounding tissue. Biological Process

Within 1–2 days, the blood loses oxygen and becomes darker.

The shifting hues of a bruise are a visual indicator of the healing stages: