Our water here is green now as soon as you fill the pool, even vinyl, and after you shock it, the green goes away as the chlorine wears off. That is because our water is being treated with chloramines at the water treatment plant. It's a process with amonia and chlorine. It's like the water comes with CC sort of.
I believe it is what has caused my problem with Iron in the water, chloramines tend to leech metals from pipes from what I have been reading. If leech is the right word.
And whenever my metal sesquesterant wears out, after I add chlorine, I get a green tint until I get the next dose put in.
Also never rule out green food coloring if you have kids around........