Water + colour = a different colour

Pale Blue and White - show imperfections, reflect light back (cooler water) but give a more beach feel
Black = an emerald green or sometimes black but absorbs energy from sun so warmer water don't show scratches and imperfections
Grey = is a nice compromise giving a greeny blue look to the water

I used a liner that had a mottled blue/black/gray/white pattern. The water color is a subdued blue, not bright, not green. I love it.
Also nice is a tan liner, looks like sand, it gives a pretty turquoise water color.