I believe that we need to reconsider the blue color as an indication of purity in swimming pools. There is a true blue and a fake blue.
And chlorinated water in a pool with a blue tint to the underlying concrete coating so to generate a blue color in a chlorine pool is a bit of a fib and a fake blue.
Chlorine is a toxin and a mutagen. Adding a blue tint doesn’t make it any cleaner :-) Or a true blue.
Just sayin’ ☺