Gold is actually a poorer conductor than copper, but it does not exhibit the same corrosion characteristics that copper does, which is why it is often used for contacts.
Silver is the best conductor you can get at room temperature, copper being second. The wire in question is most likely copper with a plating of something else so you can identify which is which. Hopefully it is not actually aluminum wire. Because you are creating a circuit (think a loop) with the speaker wire and the speakers you are limited to your weakest link. So lets say you have one conductor, a "positive" going to the speaker made of 100% pure silver and the other conductor that is your "negative" being something like... recycled beer cans... you're limited to the conductivity of those crunched up PBR cans.
I put the positive and negative in quotations because what we're dealing with when it comes to audio is AC signals, and the polarity is constantly changing with respect to what is positive and negative. Most people will argue that there is no absolute polarity with music anyway because the fact some equipment will invert the signal, different recordings are not always in the same polarity...etc...
As long as you have all your speakers wired the same, You're good

However, the speaker wire that comes free with equipment is usually best sent straight to the trash since its most likely 18awg at best. Decent copper speaker wire 12-14awg is pretty cheap relatively speaking. You may or may not notice a difference in sound quality between the two. That's a whole different can of worms.