It fades to a green or yellow hue as the body breaks down hemoglobin into other compounds.
As your body repairs the injury, it breaks down and reabsorbs the trapped blood. This biochemical process causes the bruise to change colors over roughly two weeks: Bruises
A bruise (contusion) is a common skin injury that occurs when small blood vessels (capillaries) under the skin break and leak blood into the surrounding tissue. Because the skin itself is not broken, this trapped blood pools and creates the visible discoloration we recognize as a "black and blue" mark. It fades to a green or yellow hue
Initially red or pinkish immediately after the injury; it quickly turns dark blue, purple, or black as the blood loses oxygen. Because the skin itself is not broken, this
Finally turns yellow-brown or light brown before disappearing completely. First Aid & Treatment Bruise healing - series—Healing, part 2 - MedlinePlus