This is related to the service item they just performed on my 987. Apparently they've solved the discoloration problem with these types of pieces and that's why they replaced them on my car.
Definitely looks like one of your was replaced at onep oint or another and the other was not.
Mine are semi greyed, I wonder why it was replaced thats the question. Accident maybe? I just cant imagine anyone saying, "I think I will replace one grill insert." Atleast you only need to paint or replace one now.