That's a pretty clever question, Alan ... did you once like to annoy the local priest with impossible questions, when you were a kid?
I have yet to see such a conductor coded either as a 'neutral' or a 'ground.'
Indeed, the code is written so as to make it most likely a violation were the wire to be coded green.
Since it's a corner ground, this differs from the usual center-ground on a delta system in that it is essential to determining rotation of a three-phase motor. There is no 'single phase' created when this ground is used. It's very much a phase conductor, and thus cannot be marked white or grey either.
As a phase conductor, it is required to be disconnected at disconnects. As such, it cannot be bare. As such, you are allowed to fuse it.
So, I'd either leave it un-identified, or mark it a phase color. I have no opinion as to where it should be located in sequence at the lugs. One thing that is absolutely, positively clear is that you do NOT bond it to either the panel, or any 'neutral' busses that may be present.
