What is the difference, might I ask, of you wondering who is a healer and who is a damage dealer with mages, and then looking at a black mage and a white mage in Full Af?
Who wants anyone wondering which class you are currently playing? It should be obvious, and there should be equipment that makes it obvious. There should be an identity to each class.

Having to ask just makes each class pointless. Might as well have only one class which can be made into subclasses such as "Haubergeon guy", "Robe guy", and "Tabard guy".

Color distinguishes classes, and gives them more identity.