If bruises are just bleeding under the skin, why are they sometimes yellow?
The yellow colour is just the leaked blood being broked down and reabsorbed by the body. When you get a bruise the following happens: Over the course of a day, blood seeps into the surrounding tissue while the capillaries are being repaired. The bruise gradually darkens. Over the course of a week or two, the bruise darkens to a livid red, then fades to purple, black, or blue, eventually fading to yellow and disappearing as healing progresses. Normal, light bruises heal completely in a week or two; more severe or deeper bruises may take longer. The striking colors of a bruise are due to hemoglobin and its breakdown products, bilirubin and biliverdin.
