No doubt the guy is just playing games- he wants his work to 'look professional' while not actually bothering to BE professional.
Technically, I don't think you're actually required by the code to identify the phases at all ... the entire panel could use pink wire and still be fine. I believe the requirement to identify things by voltage and phase applies only when there are more than one power system in the building- say. 480/277 and 208/120.
Ironically, I'm currently involved in a job where the opposite situation developed; the wire crew pulled in three colors, then the service crew installed a single-phase service. There goes the color coding!
As for larger sizes, I have seen increasing numbers of contractors think they're now required to use colored wire, choose to do so for a 'clean' look to their work, or who think the inspector / customer "wants" colored wires. (I'm referring to the big stuff here, too!)
Now, while we're on the topic .... why is there pink wire, but no pink electrical tape?