Outdoors, at high altitudes (especially on snow/ice) or at sea or sea shore, either the UV-absorbing atmosphere is thinner or there's much reflection of UV.
The result may be a bluish cast or low contrast & hazy far objects.
A UV blocking filter would solve much of this problem.
Also, air-born particles (water, dust, smog) may scatter both UV and part of the visible spectrum.
To reduce this haze, a UV filter is not enough. A haze filter solves this better.
It blocks both UV and part of the violet-blue visible spectrum, therefore shifting the overall color balance a bit towards the warmer hues.
With black & white, a yellow, or orange, or even a red filter may be used for an even greater effect, more penetration through haze and dramatic dark sky & white clouds.
Red light penetrates better though air-born particles because its much longer wave length.
As it zig-zags less, it bumps into fewer particle on the way, and less of it is scattered.
In all other conditions, a UV or a weak haze filter has no effect, but can protect the lens.
