When mousing over something in your inventory, signs in the background will light up. Happens on any version as far as I know.
Related issues
Comments
Ezekiel
Please do not mark unreleased versions as affected. You do not have access to this yet.
Duplicate of MC-93, please use the search function to see if your bug has already been submitted. Currently over 42% of tickets are being closed as duplicate.
dangered wolf
I believe this is related to general UI interference that does occur elsewhere (f3 Pie graph does the same thing, but instead of lighting up, doesn't render shading.)