In the least offensive way possible, I'm calling shenanigans. This game was made to be a complete departure from FFXI. When CONs and THMs were invented, they weren't meant to look or act like BLM or WHM; they've only been shaped in that direction lately. They were supposed to be entirely new standards.
There's nothing "BLM" or "WHM" about the way they dress. The conjurers wear robes, the thaumaturge wear cowls. In every color. Period.
I invite you to look at the members of the patrons lists
Here and
Here for a clear depiction. They all wear all colors. So, unless you're insinuating that Black Mages have always worn robes and coifs and White Mages have always worn one-piece cowls, you're way, way off.
The fact that most of the CONs are wearing weapons made of leaves and trees and THMs are made out of metal and bone isn't helping your argument very much either.
What you're right about is that they were originally meant to deal with the Elements (CON) and the polarities of those elements (THM) - but neither of those relate to black or white in any way whatsoever aside from the fact that their ability lists are clearly a binary of "Celestial Brilliance" and "Damnation".
Again... COME ONNNN.