The color of the sky is a result of diffuse sky radiation. On a sunny day the Earth sky usually looks as a blue gradient - dark in the zenith, light near the horizon.
Sunset is the time at which the sun disappears below the horizon in the west. The sunset is often more brightly coloured than the sunrise because there is more dust at the end of the day than at its beginning.
UV Absorbing Filters
Ultraviolet filters, sometimes called sky filters, provide a basic reduction in the UV light found especially at high altitudes where the UV-absorbing atmosphere is thinner. UV light causes a blue colour cast in photographs or loss of detail, particularly when photographing over long distances in either colour or black-and-white. Haze caused by UV light should not be confused with haze caused by airborne particles such as smog. The latter absorbs visible light as well as UV light and is not removed by a UV filter. Ultraviolet filters are made with a variety of absorption levels with some tinted to give added warmth and better colours. UV filters may be left on the lens as protection against dust, moisture, scratches, fingerprints and breakage.