vape juice changes colour when exposed to light and oxygen. This is caused by chemical reactions that cause some breakdown of constituents. Although nicotine e-liquid for DIY mixing does turn a very light brown with age, most colour changes are caused by other ingredients, flavourings in particular. Many vapers deliberately expose new
vape juice to heat, light and air as this changes the flavour. The colour can eventually become black or near-black for some flavours and I have had a particular vanilla custard that was at its best after 6 months storage when it was almost black in colour.
Without nicotine you will probably find that some flavours change colour very little, others do so to a much greater degree. Nicotine is not the main cause of the colour change. The recommended method for reducing change as much as possible is to keep it in the dark, preferably in brown glass bottles, keep it cold and top up bottles with an inert gas and use an airtight cap as well as keeping it in a fridge or freezer for storage.
Probably eventually the taste will change if you leave it long enough. Plastic bottles are not a good method of storage as plastics can leach into the liquid. Unfortunately in the EU the new TPD, which includes e-cigarettes and everything associated with them, even if there is no nicotine, will only allow tiny plastic refill bottles, if they aren't banned completely.