What's this addon do?
It stops the UI from desaturating (graying out) the items in your inventory while engraving a rune.
Why does that matter?
When you cast a rune engraving spell, the items in your inventory are grayed out (desaturated) if they're not valid targets of the spell. The API is bugged and will continue to tell the UI that we are casting the spell even after cancelling the cast. This is why when you re-open your bags, all the items appear gray again!
Does this addon "fix" the issue?
It doesn't really - it just stops the items from being desaturated (grayed) anytime you use the engraving system.
What's the downside?
If you are trying to engrave a rune onto a piece of gear in your inventory (as opposed to an equipped item), all the items that are not valid targest to be engraved will not be desaturated (grayed). This *might* be an inconvenience for some people.