There are several shades of zinc plating, if brightener is not added, the parts come out a dull gray. Also consider that zinc plating will fade over the years, especially 50 years. Also, as we all should know, service replacement parts may or may not hit the mark on matching what was used on the assembly line. And also consider different vendors supplying the same part, but minor differences, including final finish.
In response to this thread, I was more interested in design changes as a car I restored was recently judged and a point taken off for 'incorrect spare tire wing nut'. No idea if that was for the design being incorrect or the finish.