On my car they were originally gold in the center, but after years of fading they almost looked silver. I know that my emblems were original since the car has been in the family since '65.
I too have seen both colors used on other 64's. Have also seen certain articles that say the silver is correct and yet other articles say the gold is correct. Maybe Ford used both colors back then and used one color on converts and another color on hardtops or something like that. Just not 100% sure. All I know is what color my car came with so that is what color I replaced them with.