Template:Featured:Armor Dyes
There are 18 known colors of armor dye in Diablo 3, plus two special types; dye remover and transparent dye (which makes the item not display at all). Players find or purchase dyes in the game, then use them to recolor their equipment. Dyeing (not dying) will modify the color of an item; not the whole thing, though. Just some portion, often a border or sash, or else the background of an item while the metal remains a silvery hue.
You can read more about the Armor Dyes and view the armor dyes and the lore entry for them including screenshots showing off every dye in action, with before/after views of the same character.