General rule for flavored
vaping juices is cool, dry and dark, but most juices will be fine just sitting around at room temp. The most unstable components of a flavored
juice, other than the inevitable trace oxidation of nicotine, are the flavors themselves, generally a reaction with water that is in the juice. Fridge will not help this, if it going to occur, but this is generally an infrequent event. And the cold from the fridge will promote water condensation into the juice if it is opened while cold. There have been a couple rare instances from the early days of
still-sealed flavored juices going bad in the fridge after 6 months...the fridge is likely not the culprit, the reaction would have happened regardless.
Best to not buy more juice that you can vape in a month or so. I make my own DIYs, and store the high-nic unflavored juice undiluted in freezer, but I only make enough juice for vaping to last a few weeks, at most. Never had a flavor go bad, as in vinegar and wet dog tastes, which are the common results of flavor decompostion, but many flavors
will fade over time. My chocolate juices I made six months ago barely taste at all now, but they are still ok to vape.
Coloration from nicotine oxidation is generally unavoidable over time no matter what you do. The actual amounts of oxides are generally extremely low, barely a change in nic content, but they can turn a juice yellow, pink, or dark brown. They are not harmful, however, just strongly colored.
