A friend of mine has a boat (Sea Ray) with a dark blue hull. He said "never again". It looks great if it's been freshly detailed but after a few months it begins to fade and looks bad.
My boat is a light tan (Almond, more or less) color and it fades but not as bad as his.
White fades a bit but it's not really noticeable. White also reflects heat from the sun and the interior is cooler. White is also easier to match if repairs are necessary.
Black, dark blue, red, etc. look great when new but not as they get older. Also, colors go out of style, white does not. Remember the orange and maroon boats of the seventies?