From what I remember change in colour is due to the nic being exposed to oxygen, so it can't be avoided in most situations, I wouldn't worry about it, changing colour is all its doing 
I have a bottle of fish flakes (goldfish sauce) that started out life quite clear and now looks like a bottle of irn bru
As I rarely vape it, its just sat changing colour, when ever I have the occasional blast of it, tastes the same as the day I bought it.
Tried something new this morning, built a 'turbo coil' build, 22g on one side, 24g on the other, 7 wraps each, easily one of the nicer vapes I've had recently

I have a bottle of fish flakes (goldfish sauce) that started out life quite clear and now looks like a bottle of irn bru

Tried something new this morning, built a 'turbo coil' build, 22g on one side, 24g on the other, 7 wraps each, easily one of the nicer vapes I've had recently
