I would be shocked if one was grey and the other was black but they were both grey/greyish. I bet you have two people Q/A one on the left/right and they are verifying each side of the vehicle. Hell like you said, it took you 3500 miles and how many times just drooling and staring at your truck for you to finally realize it was wrong. A vast majority of my autos would be considered luxury or "highend" and even they have been know to have a slip up now and then. My 2004 BMW 545 M sport was delivered missing an entire module. The only reason it was noticed is because in 2004, I actually used Bluetooth and I could not get it to work(yea I am a tech guy).