The transparency has gone.
Black background also observed when holding the item in hand and on the ground, but an actual bell block is fine.
MC-163003
Bells in the creative inventory have a black background
Resolved
Duplicate
0
Lefty Power123
(Unassigned)
Unconfirmed
(Unassigned)
19w41a
Retrieved
Thanks for the report; however this is a duplicate of MC-163001 (it affects several items, not just bells).