It really depends on the specific cable. I don't subscribe to the ideology that copper = warm and silver = bright. I've tested a ton of cables and pairing really depends on cable to cable. I can list several cables that defy that ideology. You cannot guess how a cable would effect the sound just by looking at the material. I personally would recommend going with a high quality UP-OCC or OCC Litz based cable because they have a quality of clarity that IMO is a step above regular cables. Several manufacturers offer them. Choose the one you like, one that falls in your budget. No need to spend a ton of money on the cable. Nice cables can be had for fairly decent money. I personally use Ego Audio Beer and Whiskey with the Elex. You can check out Effect Audio, PlusSound, Eletech, Ego Audio, Satin Audio, etc. Even if they don't offer 3.5mm headphone connectors in their product page, just shoot them an email. I'm sure they'll make a cable for you as per your specifications. You can also shoot a PM and check with
@doctorjuggles, who is the owner of the up and coming Khanyayo cables and makes really nice cables. He's a nice guy and quite popular in the forum.
Ear Audio from India makes sick custom cables too. You can connect with him through his Facebook page if you like.