Thanks for the query.
The skin of shaft is loose and there is chance of collection blood following surgery.
This might have lad to bluish discoloration of the shaft.
Dont worry, just wait for some days this discoloration will settle down on its own.
Please meet a dermatologist
for exact diagnosis.
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.