Why would a new switch come with aluminum wires?
I would guess that that's tin, or some other solder alloy. 

Coating copper in tin makes a surface that wont oxidize as much (or in the same way, I'm not sure). This is good when you're expecting to need a surface contact later. 

You can tell if that's what you're seeing, by snipping the end off with some (sharp) clippers. If the cut is clean, you should be able to see whatever metal is in the middle. I don't know of any reason not to do this, but that doesn't mean you should.