Yellow semen??

So my boyfriend and I use condoms and when we fall asleep straight after sex we sometimes just leave the condom next to the bed on the wrapper.

We accidently left it for a few days (gross I know, don’t judge 😂) and when I came to pick it up his semen in the end of the condom was literally bright yellow.

I’m wondering if cum can go off? Maybe old semen goes that colour? Or if it was something he ate or drank? Or if his semen is unhealthy and this could mean he’s in fertile 😔

None of his other semen I have seen has been this colour. He’s not the healthiest guy, smokes a lot of weed and doesn’t eat well. This could be the reason.

Anybody know anything about this? Please help xx