Pool water that is clear and clean, will look very blue in swimming pools that are clean white.

Compared to WHITE pool walls, blue colored walls and floor will
+ make the pool water look darker;
+ increase pool water temperature measurably;
+ possibly make the pool water look bluer when the water is hazy.

I once painted a Girl Scout camp pool (200,000+ gallons) with Kelley's Zeron epoxy in "Viking Blue" (very dark blue) and got a 6 - 8 degree increase in temperature. In Chicago, that might be nice -- in Miami it would be terrible. On the downside, the water looked dark, and the paint would chalk off onto swimmer's feet, early in the pool season.