The water color hue for a dark color pool finish is highly influenced by its surroundings which make predicting the water color hue difficult. The hue cast can vary from green/blue to blue/black. Dark colored pools are reflective and will mirror the landscape, which can create ambiance for an early evening poolside conversation with friends. One of the disadvantages of dark colored finishes however, is that scale build can be very pronounced on the surface if the water chemistry gets off balance. More attention to the water chemistry is the key to keeping a dark colored pool finish looking good.  A good analogy might be to purchase a black car.  Dirt and grime show more up more on a black car versus a light colored car but, wow those black cars look incredible.  A disadvantage to some and an advantage to others depending on the climate is that the water temperature can be a few degrees warmer that a light colored pool finishes. For those that want to extend their swim season this is the desired outcome.