Item colour was used back in Vanilla to show gear power as Ilevel was not shown. Greens for quest items/random drops Blues for dungeon/higher quality loot and epics for random world drops and high end PVE/PVP loot. Now it is only used to show item power nothing more.
Vanilla legendarys were pretty well fare aside from the crafting required which if you were poor or in a small guild would be a bit of a hassle to get.