I think it would be a great idea to allow players to customize each eye individually, as it would let players give their characters more personality.( or just to make them look cool)
Differently colored eyes would also help with customizing aspects of certain classes, for example:
A warlock has made a pact with a succubus, she wishes to see the world through the eye of the warlock , instead of the customary price of the Warlock's soul. A part of the pact then includes that the succubus gets to see out of an eye of the warlock, causing the warlock to have an average blue eye in one socket, but a demonic yellow Eye in the other.
As usual, something like this does not require a change to the class itself, but instead, it can be accomplished through more customization options.
