Not intentionally trying to get this thread back on topic, but nicotine changes color when exposed to oxygen. My atty's do the same thing as the OP's, and the ones with higher nic levels do it quicker. Even so, my rda with 3mg looks like that in just a few days.
Now, to get back on the K word topic, this is what I carry.
A thread can have more than one topic, right?
I do know that coils change color eventually , but as I said in my previous comment i found where the rust was coming from and mine was striaght up red looking just like blood .