Yes, the more opaque the cover (especially to UV), the lower chlorine loss from sunlight. The downside is that you'll also get less heating of the water from sunlight so may not get the pool water temperature to be much hotter than the average day/night temperature if it's too opaque. If it's more opaque, then a darker cover plus water circulation can still heat the pool somewhat, but a mostly clear bubble-type cover heats the best (though doesn't protect chlorine loss very much).