Thanks for the query,
Swelling and discoloration might have appeared due to hematoma
There might be an injury
to vein leading to leak of blood and collection under skin.
Usually it resolves on its own in a month,
If it persists, drainage
may be required.
Let me know if you have any other doubt.
you can ask a direct question to me on this forum, following the below link.
Wishing you a good health.