Colored Glass panes and colored glass are not transparent when holding them. Also you can see the other side of it, making it buggy. In a normal glass block, you see only the side facing you.
Linked issues
duplicates
Comments
_zombiehunter
Stained Glass not being transparent as an item >>> dublicate of MC-10633
Stained Glass showing all sides >>> NOT A BUG >>> MC-34649
Normal Glass NOT showing all sides >>> inconsistency issue >>> MC-34751