Why are inventory items occasionally highlighted?

Solution 1:

Newly picked up items are highlighted in your inventory. After picking up a new item, it will stay highlighted until:

• You mouse over them in your inventory
• Approximately 2 minutes passes after opening you inventory

Simply opening/closing your inventory does not change their highlighted-ness, but items will not de-highlight until you open your inventory. I.e. the 2 minutes do not start until you see the "sunburst" around the item when you open your inventory

Stackable items will also be highlighted in both your inventory and stash when a new stack is formed/updated. For example, if I have one Topaz in my stash and one in my inventory and I right click one of them, the newly formed stack of 2 Topazes will be highlighted wherever it ends up.

Splitting a stack will only highlight the newly placed stack, but most of the time you will have your mouse over it anyway. If you place the new stack and then move the mouse away quickly, the stack will be highlighted.

All item highlights will be cleared upon leaving a game.

Solution 2:

These are new items that you've picked up since the last time you've opened your inventory.