As shown in the attached image, when you have an item in the hot bar, it creates some weird coloring (color seems to associate with the item)
Class in the hot bar doesn't seem to appear transparent.
The Potion seems to expand its "enchanted" over lay to fill the entire slot.

This occurs when using one of the "Super Secret Settings" Shaders, if you aren't using any shaders it returns to normal.

-Hope this helps
Bud G.