I’d ask your hairdresser – there are lots of specialist products around these days.

I think it is supposed to be the copper that collects and causes a green tinge. I have blonde hair and the same thing used to happen to me as a kid, though I wasn’t worried about it as it fades after time. My son has dark hair, and while he is always at the pool, he never has had that problem.
Now I always wash my hair with shampoo straight after swimming and that seems to help. I’ve heard that adding acidic substance such as vinegar or lemon juice while washing can help. And wetting hair with normal water before hand can also help. And certain pools are worse than others due to pH balance being out, so you could change pools if you are worried about it. Or use a swimming cap. Sorry you might have tried all of this, hope some of it was helpful!