Not Medical Advice: It could be a result of stretched skin due to swelling. Initially the bruise appears shiny and red but it later changes color to black, blue, green, yellow and finally fades away.
A bruise, also known as contusion, is a blunt, compressive injury that does not involve a break in the skin. It is a type of hematoma of tissue in which the blood seeps out of damaged small blood vessels (capillaries) and collects in the surrounding tissue, forming black-and-blue marks beneath the skin (ecchymosis).
Bruises cause damage to the skin and underlying soft tissue. After injury, gravity may pull blood downward so the ecchymosis may extend some distance from the contusion site. Over a period of days, the black-and-blue marks beneath the skin will change to green and yellow due to degradation of the extravasated blood components, and eventually fade. Muscle contusions are common although any organ in the body can sustain a contusion injury.
Learn bruises treatment and first aid information at WebMD.
Tip! Find out things you can do to prevent or minimize bruising after an injury at MedicineNet