Quest: Color Your World

You can obtain this quest anytime after lvl15 by going to Vesper Bay in Western Thanalan.

The Dye option appears in the General section of your Skills&Actions menu. To use, have a dye ready. You can either buy them from npc vendors in town (dyemonger, and some other merchant names I forget) or craft them. Then select and you can change most crafted items in your inventory. Aetherial, Dungeon drops, and Philo/Myth armor cannot be changed.