Chromatic Orb reforges the colour of sockets on an item.
A Chromatic Orb is a poe currency item that can be used to re-roll the colour of sockets on a weapon or piece of armour.
How to use Chromatic Orb?
Right click this item then left click a socketed item to apply it. Shift click to unstack.
How to obtain Chromatic Orb?
(1) Like most currency items, Chromatic Orbs can be dropped by slain monsters, chests, and destructible containers. They also drop from Arcanist's Strongboxes.
(2) One can also obtain Chromatic Orbs directly from vendors. Yeena will sell a Chromatic Orb in exchange for 3 Jeweller's Orb, and Tora will sell 20 Chromatic Orbs in exchange for 48 Jeweller's Orb once daily.
(3) Chromatic Orbs can also be obtained by vendoring an item with one socket of each colour (red, green, blue) linked together. This is one of the most common ways to obtain Chromatic Orbs. In particular this means you can get some Chromatic Orbs cheaply (typically for about one Orb of Transmutation each, or less) by buying such linked items from the Vendors.
How to Spend Chromatic Orb?
Chromatic Orbs are primarily used to change the colours of sockets on an item. Sockets are more likely to roll a colour corresponding to the attributes of the equipment being altered. The higher the attribute requirements, the more likely it is to roll the relevant color: red sockets for Strength, green sockets for Dexterity, and blue sockets for Intelligence. It's only possible to get red, blue or green sockets using this orb; for white sockets it's necessary to use a Vaal Orb.
If one either wants to avoid randomness, or wishes to obtain a specific colour combination that is unlikely on a certain item (e.g. getting all red sockets on an item requiring high intelligence), one can instead use the Artisan's Bench provided by Vorici. When obtaining socket colours that an item is already biased towards (e.g. obtaining red sockets on a chest piece requiring high Strength), using Chromatic Orbs manually is less costly than using the Artisan's Bench. On the other hand, for obtaining a socket colour that an item is biased against (e.g. obtaining green sockets on a chest piece requiring high Strength), using Chromatic Orbs manually is typically much more costly than using the Artisan's Bench.
When Vorici is level 8, these recipes can also be applied to corrupted items at the cost of using one Vaal Orb for every Chromatic Orb required. This is currently the only way the colours of sockets on a corrupted item can be modified.
PoE Currency Guide:
https://www.youtube.com/watch?v=uecOA6hJYRs