You know,,, I think ALL TOO MUCH has been made of this. The Grey one work FINE for most people (I'm sure 99% of the 7.3's out there have them without their owners ever noticing a difference)
The Black one are actually the Most unreliable ones out there! Yes, there are apparently subtle improvements to the way the engine runs, but at this point because the Black ones are now so rare, I think it's become a moot point...
I assume you've been steered by this info -> Black, Grey, & Dark Blue Cam Position Sensor Perdels Test - Diesel Forum - TheDieselStop.com
My guess is, most people would not
notice any real difference with any of them in the way their truck performed and you should not be so concerned about finding just the "right" one