That is a not smtg out of e ordinary.
Nicotine will oxidize and change colour, not potency, thru exposure to heat, light and also air. So, even yr cartos, clearos and atties will help e e-juice to oxidize.
For some users, they would leave e bottle open to steep overnite or over a few days. some would just put it in a bowl of water and nuke it for even quicker results. Try it! Steeping works!