This is normal with all tanks n such. The liquid will heat up and it will discolor and get darker. Some people do not vape this as the flavor might change. With the tobacco flavs I have been vaping, it does not change flavor.When my liquid turns a little dark in my T2, is that bad? I see it when it's low and sits overnight mostly. Anyone getting this?
Also, sometimes it gets dark from the coil gunkd up. This is the case when it darkens soon after refilling. Then time for a cleaning/dry burn.