From time to time I've seen '67 and '68 Mustangs with amber fog lights, and the amber bulbs are listed as an original part in the National Parts Depot catalogue. My understanding is that all fog light equipped '67s and '68s came with clear bulbs, and that amber ones were an available after market part that grew in popularity in the '70s. Is that right?
I've also heard they were a state-specific requirement (like California required them to be amber or something along those lines).
Were amber fog lights ever installed on a '67 or '68 Mustangs from the factory?