What he's using is basically an off brand ego twist/clearomizer, if it really bothers you that much try a TC mod, set up right it won't be able to burn your wick so you can stop worrying about this issue... Maybe a different clearomizer too.
in my rta's when I'm not using TC, the cotton usually takes about 3-4 days to start looking brownish, then I replace it. That's about normal for heavy use imo.
btw theres nothing harmful here, my gf lets her coils get way worse before rewicking. So yeah, you have a thread full of answers. Something tells me you won't listen to any though. lol.
he doesn't like any of those... there's a whole other thread dedicated to that...