When an injury such as a sprain or a break tears blood vessels enough to cause bleeding, the blood does clot. However the material (including red cells) forming this clot is subsequently broken down and the hemoglobin itself is further broken down into substances of various colors.
The (broken down) hemoglobin in the tissues migrates, usually in the direction of gravity along fascial (connective tissue) planes and frequently pools near fascial attachments. A bruise in the leg, for instance, might eventually show up as a discoloration along the border of the medial and lateral heel area. etc