I know people will say it is copy of FFXIV. but why not? it will not be the first or the last time Blizzard takes idea from different game and add their own version?
Basically it works like this, first you do a simple story questline to unlock the dye system which will be part of the transmog system.
Then Blizzard should add a lot of colors and dye into the game from different contents of the game like from dungeons, raids, reputation, npcs, rares, and even old contents. Just like how they add a lot of pets in the old contents of the game and new.
Maybe not everyone care about such thing but I am pretty god damn sure a lot of players still want that red cm paladin set from datamining!
Such a simple system will make players playing the game more and more!