Explorer Vision is a major Feature in Patch 1.3.1.2 ...

When closing the Map, for the remainder of the turn, all generic Icons for Items that you've discovered will show their actual Class!

Items you haven't picked up yet and therefore don't know their Class, will not be affected. The highlighting also tells, whether they're damaged (only applies when you already "know" that they're damaged, a.k.a. inspected them at a Fireplace). Consumables, that are nearly depleted (1 Charge left), will also show up with the "damaged" Highlight.

If  one needs to find a new Weapon or Shield, this should be a welcome QoL-Feature. I have tried displaying the  actual Class all the time, but it did not work from an aesthetic standpoint: it looked bad and cluttered, too much information to take in with a glance, and then I really don't want to trivialize  the notion, that you have to memorize parts of the layouts and placements to play effectively.

It is a reasonably restrictive mechanic, you still have to collect both Map Pieces, and the surrounding has to be illuminated for "Explorer Vision" to work, so when entering a new Region, there is still mighty incentive to explore without getting spoiled.

Also mind, that using the Map takes a Turn, so you're better off not using it in Combat!