I had this happen with QSC Deca bought end of last year. Was clear when it arrived, slowly turning yellow. This kind of happens with all.my QSC gear over time. Haven't noticed potency issues. Also, i had a vial of test e from QSC laying around from 2 years ago unopened. It turned too yellow for my liking and when I smelled it, it kind of reminded me of something sweet, like cinamon. QSC back then told me to toss it. Not sure what process causes this degradation maybe some of the smarter members can chime in.