When you reach refinement levels of +5 +9 and +13, your equipment will receive an additional stat. You’re able to see these additional stats by pressing the shift key and hovering your cursor over your equipment in your character menu.
Gear has 5 quality levels (aka Hidden Stats), marked by their color. From lowest to highest they are: gray, green, blue, violet and gold. Green items are from killing monsters in the open world and in dungeons. Blue items are earned from completing certain quests. Violet items are earned in dungeons or by killing bosses in the open world. They can also be purchased for city reputation, honor points and Order of Guardians' reputation points.
The most valuable gear in the game is gold. It can be obtained for honor points, if your character has achieved the required PvP rank, or for Order of the Guardians' reputation points. You have to create the very best gear yourself. You can obtain your first set of such armor at level 37, after completing a special main storyline quest and collecting or buying resources. Items that are created have higher stats than regular golden items. In addition, once a hero achieves a higher level the gold items created can be remade and their levels boosted while keeping extra improvements.
As the gold items created are the most powerful in the game and improving items provides more opportunities to perfect them, the items obtained in raids are not an end in themselves. Often violet items and lower quality items are used as resources required to upgrade gold items.
If you are unsatisfied with the stat that you were given you have the option to re-roll this by using the Venerate Renew option at the Refinement NPC. This will, however, cost you refinement materials. Hidden Stats will also be transferable to new equipment if they can be applied to that particular equipment slot; otherwise, a new stat will be re-rolled.