Colors and quality levels

What do the quality levels/colors of the gear mean? Pink/green/blue? What are the rarities?

pink is low lv upgrades. (item lv 2 higher) green is 5, then blue is 10 to 20 higher.
but even if item with lvl 18 and pink lv 2 is should be same as character lv 20 it is usualy higher same as item lv 24.

Sorry but I didn't understand that at all! Do you have a link that explains it maybe?

There are 4 different colors of gear,

Pink- Atherial Gear- Pink Gear is pieces of common usually craftable gear that have random augmented stats attached to them. These are by no means special most of the time, but every now and again you can come across a special gem that has some really good bonus augments attached.

Green- Scarace Gear- Green Gear is special gear that has a higher than average stats and item levels compared to gear of the same equippable level. You can kind of think of these pieces of gear as a HQ +2, but they are not by any means leaps and bounds better than normal gear for their level.

Blue- Rare Gear (Not to be confused with R/EX)- Blue gear is special gear and usually has a much higher stats over Scarace Gear. This type of gear's item level also varies greatly, and typically you won't see any Blue gear that has an item level below 50.

CONT:
Purple- Relic Gear- Bluntly put, Relic is a special type of gear and is considered to be the strongest in the game, giving unique and powerful effects no other gear in the game can provide. You might think of Relic gear as gear specifically attuned for your class/jobs strengths and weaknesses. As of right now the only Relics out there are the Relic Weapons which are only avaliable currently for the original 1.0 Jobs.

Sorry, hit character limit.

well lets try to explain

see this. http://ffxiv.gamerescape.com/wiki/Ae...Velveteen_Cowl (in the upper side it say ltem lv 27) while usable lv is 25
while this http://ffxiv.gamerescape.com/wiki/Velveteen_Cowl (in the item it say item lv 27) and usable by a character lv 27 check the stats and you see its more than only 2 item lvls.

and all the gear have this dispresentations.
but easy to think on the item lvl is pink, 2lv higher, green 5 and blue 10-20 ( also based on level of the gear, low lv pink have 0 lv higher. and low lv greens have 1. this change around each 10 lvls. unless pink that have max 2 lvls.)