Is it normal for homemade vegetable stock to turn green? I made it yesterday and then it was a light greeny-yellow colour. Now it's bright green.

What did you put in your stock?

Yes and no.
There was a thread on Reddit about 10 yago, tracing similar result to herbs in stock.
Too early and pervasive to be mold.
If youre brave, taste and see if you like result. Also can you figure out ehat in pot caused it.
If you're concerned about safety, consult nutritionist or other professional source or toss.

The color depends on the ingredients.

I make vegetable stock from time to time and it's never green. I usually make it with mushroom stems, some carrots, onion, celery. Herbs like parsley stems are sparingly added.

I've also had vegetable dashi from the packets the local Japanese grocery store sells. That isn't green either.