devo had nailed it.
The outer plating of the socket does not need to be gold plated (altough in many cases it does) as it is soldered right into the board, there can be many variations as to the silvery looking plating, in most cases Tin is the main metal composing the alloy.
The pin metals are usually of high ferrous based alloy (such as Kovar) with a thick Nickel overplate (and a Tin alloy plating over it).

The indise hollow part of the pins will always be gold plated as they serve a removable component (CPU) with all the abuse that come along with it.