The color changes in a bruise are due to the breakdown products of hemoglobin. Initially, the bruise appears red due to the presence of oxygenated blood. As the hemoglobin breaks down, it forms biliverdin (green) and bilirubin (yellow). Eventually, hemosiderin (brown) is formed, which is a storage form of iron from degraded hemoglobin. These transitions are reflective of the body's ongoing efforts to clear and reabsorb the extravasated blood.
