I've always noticed I used less chlorine with the cover on. I don't know how much is due to UV blocking and how much is due to inhibiting evaporation. I don't KNOW that clear covers don't block UV. Clearly auto glass does--ask anyone with photochromatic eyeglasses--they only change in direct sunlight (the old glass lenses changed in the car--the new plastic ones don't). Blue PROBABLY blocks UV better, but, again, I don't know.

Clear allows more light to reach the water, heating more, but the greenhouse effect of both is important, as is the insulation qualities.

But I've also found that cheaper covers fall apart after 3 seasons, but the expensive ones always go a 3 full years, and the warranty NEVER covers what fails--just the seams....So I now go with the cheaper ones, which are also easier to carry on and off when the season begins and ends.