if you go into a version prior to 14w07a the texture in the inventory of the beacon is very transparent and looks good.
if you go into 14w07a the texture is more white-ish, the glass is much less transparent.
not sure if it is really a bug, but it is worth checking
Linked issues
is duplicated by 8
MC-48468
Beacons have no shading+contrast when rendered in inventory....
Resolved
MC-48478
Item Beacon diamond block part appears black
Resolved
MC-48588
Beacon texture changed
Resolved
MC-48910
beacon and end potral frame have dark textures in inventory
Resolved
MC-49642
Part of Beacon Item Not Viewable
Resolved
3 more links
Confirmed