In any case, after each playing I wipe down my guitars *and* the strings and fretboard with a clean, dry cotton cloth. And once a week, I use a device called, "The String Cleaner - the ultimate string cleaning tool" made by ToneGear (see here, http://www.thestringcleaner.com/ ). Amazon offers 'em for $11, http://www.amazon.com/The-String-Cleaner-by-ToneGear/dp/B001FSZR4U/ref=sr_1_1?ie=UTF8&qid=1342478176&sr=8-1&keywords=the+string+cleaner .
I seldom have what I call tarnish on my acoustic strings (Elixir Nanoweb) but when I do the pad gets rid of it. I haven't noticed any discoloration on the electric's strings but they get the same treatment each weekend too.
FYI, I find The String Cleaner very quick and easy to use...cleans 360° and no solutions/liquids.
"It takes a lot of devotion and work, or maybe I should say play, because if you love it, that's what it amounts to. I haven't found any shortcuts, and I've been looking for a long time."
-- Chet Atkins
-- Chet Atkins