Unless you are concours owner, shouldn't be any difference. Even then, unlikely judge could see any error. I have one original and one replacement from local auto parts store. Can't tell you which is which. Maybe if I disassembled light.
I can't remember the last time we disassembled a foglight for concours competition
. Unless the replacement has some oddball color other then silver you should be safe. If a concours judge asks and you admit to it in DIV II then no deduction because it still looks the same . If In DIV I concours ,yes there will be a deduction. In that circumstance I would plead the fifth amendment.
If the judge can't tell then he can't tell. Maybe if it is killing you knowing that a replacement part is on your car when every other part on your car is factory original including Battery ,tires battery cables etc. I would also replace it with genuine .