Testosterone turned yellow near the rubber stopper when stored in syringe, refrigirated since 10 days

I'm storing it in the fridge at around 10deg C, for 2 weeks. I transfer small amounts from this 27 G syringe to a 31 G to injec. Noticed yellowish tint today, mostly near the rubber stopper, is that normal?

I store it vertically with a air bubble so thst rubber never touches the oil.