Nice shot! This bird looks like A85 which was ringed on 29 Oct 2018.
HKBWS are conducting bird ringing at Long Valley during Oct-Dec 2018 with the permission from AFCD. Please see following for further details:
http://www.hkbws.org.hk/BBS/viewthread.php?tid=27687&extra=page%3D1 If you have any sighting records for the color-ringed Bunting species, please report those sighting here. Thank you for your contribution.