Item Color Types

[MetatronPrime]

What do the colors of items mean such as blue, green, etc.

[AnimaAnimus]

Pink is aetherial gear, basically standard gear enchanced with aether so they get a stat boost. Stat boosts are also randomized so they can sometimes be better than green.

Green is the standard dungeon gear. Better than NQ crafted, usually about as good as HQ crafted. Also the color of star-level crafted gear. Has a unique look.

Blue Gear is considered rare, usually tome gear and raid gear, better than crafted and generally the best gear for that slot of that level with few exceptions. Almost always the gear of the current level cap. 50, 60 and soon 70 I'm sure. Usually roll or job specific. Think of it as +2. Anything crafted can only match or surpass this gear with forbidden melding aka 5 melds.

Purple are relic and artifact gear which is restricted to weapons atm but Yoshi said they are thinking of adding full gear sets to these in stormblood.

[Enkidoh]

As above, the colour of the icon is a basic indication as to how special and rare that piece of equipment is - AnimaAnimus has got most of it right but a little clarification is needed.

White or 'grey' gear is your basic equipment - this is gear that you can buy from a npc vendor for gil or can be crafted. White gear can come in both 'normal quality' or 'high quality' versions, the HQ version designated by an unique symbol next to the item's name and a discoloration of it's icon. White gear can mostly be sold on the Market Board, converted into materia or have materia melded to it, although there are exceptions to that where there is special white gear that is 'unique' and 'untradable' and thus cannot be sold on the MB.

Pink or 'aetherial' gear is the next step up - this gear usually has the same appearance as 'white' gear but has the word 'aetherial' added to it's name. Pink gear is usually found in dungeons and from treasure chests during levequests. It cannot be sold on the Market Board, but can usually be converted to materia. It can also be traded in at a Grand Company for Grand Company Seals. Pink gear is unique in that besides the 'base' stat equivalent to the normal white version of that piece of gear, atherial gear can also have additional stats that are random and thus two items with the same name can have totally different stats on them). Hence aetherial gear can be often better than white gear.

Green gear is special gear - as mentioned it's usually found as dungeon drops but can also be quest rewards and bought from special npc vendors such your Grand Company. Green gear usually has a unique appearance and thus often has special stats. Most, but not all, green gear is unique and untradable and thus cannot be sold at a Market Board. Green gear can be traded at a Grand Company for GC seals.

Blue gear is usually among the best gear in the game - this includes quested and vendor 'Artifact Armour' (AF) that is Job specific, the premium (paid) wedding dress, and other special vendor gear. Equipment bought with Allagan tomestomes from the vendors in Revenant's Toll and Idyllshire are almost always blue gear. Blue gear is almost always Unique and Untradeable and thus cannot be sold on the Market Board. It cannot be converted to materia however some blue gear does exist with materia slots. Blue gear can be traded at a GC headquarters for GC seals.

Purple gear is 'special' gear and apart from one exception, is almost exclusively for 'relic' weapons and 'anima' weapons and their upgraded forms. The exception is the wedding ring the Eternity Ring, which is considered purple gear probably because of how 'special' it is (besides being a symbol of bonding between two players it also has a unique teleport ability). Purple gear is unique and untradable and cannot be sold on the Market Board or converted into materia.

That's basically it in a kuponutshell. If I've made any mistakes please correct me!