Hello,
This may be due to bruising of skin which may occur after trauma to the skin. The blood under the skin which causes the discoloration of bruising should be totally reabsorbed by the body in three weeks or less.
If the symptoms persist for a long time, then it may be due to formation of hematoma because of blood trapped in tissues. This blood may need to be drained.
I hope it helps. Take care and regards.