Placement of Commas
Solution 1:
The current standard for education purposes, what a high school English grammar book would teach in the US, is use of the Oxford comma. [S]ilver or black metal is actually a single entity in the series. [S]ometimes all three is the third member of the series with gold being the first member.
This is why the SAT had the second answer. I taught SAT for a review company for a few years; the Oxford comma is a frequent topic, and since it usually is skipped in newspaper, even in the US, it is just one of their "tricks."