Is the best color of solar cover black blue silver or clear?

Black solar covers are the most efficient at raising pool water temperatures.

Solar pool covers work by absorbing solar radiation and transferring it to the pool water. Dark colors, such as black, are the most efficient at absorbing solar radiation. Blue and silver solar covers are less efficient at absorbing solar energy, so they will take longer to raise the water temperature. Clear solar covers do not absorb solar radiation at all, so they will not raise the water temperature.