1) Just as a precautionary question: the rest of your setup is the best it can be, right? Including amps and source material (DAPs). Going from memory, getting new headphone cables cleaned up or changed the music but buying a good portable amp and DAP really made more of an improvement overall.
2) Now that I've gotten that out of the way, because of the warmer sound signature of the SE535's, I would highly recommend silver as a material of choice. The 535's are intimate, slightly neutral, but the treble is rolled off. The worst thing you can do, IMO, is increase that warmth.
3) I don't know how different actual silver cables will sound from each other, only from the "standard" copper that comes with everything, that's something I'd recommend you do a lot of reading over: does a Toxic cable, for example, sound that much better than a silver costing half the price.
4) Lastly, the aesthetics matter a lot to me. Make sure you get something durable and relatively thick (even if it's just the covering) to give the IEM a premium feeling. Aesthetics matter "almost" as much as sound