Cascades to Coast

Why do bruises turn yellow

When blood is not exposed to oxygen, it appears blue, as you can see looking at the veins on your arm. A bruise first appears blue because the capillaries and veins are broken underneath the skin and the blood is released. As the blood (hemoglobin) decomposes and is reabsorbed into your body, it changes color. It starts of as a blue color, but slowly the hemoglobin is broken down into other molecules, which are different colors: green (biliverdin) and yellow (bilirubin). The bilirubin molecule is what appears as yellow.