There's no right and wrong with this, IMO. However you choose to do it, keep that configuration the same for all terminals at each speaker and at the receiver. That keeps the polarity consistent. If you decide to connect the silver end to the black (negative) and copper to the Red (positive), do that everywhere.
As far as I know you won't fry anything if the polarity is inconsistent, it just won't sound right. Bass will sound weak. Heard about this from a friend. 😃
Should add, don't touch the silver and copper wires together when the opposite end is connected to your amp or receiver. A lot of amps and receivers have built in protection against this, but don't count on it.