Atmospheric Perspective reproduces the way far things look less colorful and distinct than similar near things. For example, whenever you paint a distant line of mountains blue and a nearer hill green, you are utilizing atmospheric perspective.
Below, notice how color changes and edges soften with distance. As light travels through the atmosphere, it is blocked by dust particles and bent or refracted by microscopic droplets of water that act like tiny prisms. The scattering of light rays makes distant things look softer edged and out of focus compared to close objects. The refracting effect of moisture in the atmosphere accounts for the way distance changes all three aspects of color—hue, value and intensity.
Hue is determined by the wavelength of light. The shorter wavelengths such as reds, oranges and yellows are refracted by water droplets at more acute angles. So the warm colors are the first to drop out with distance. They literally can’t punch through the atmosphere to reach your retina. They get diffused and scattered and disappear. The longer wavelengths such as blues and violets are refracted at shallower angles, so they can push further through the haze. That’s why distant mountains look blue or violet.
The value range of objects becomes narrower and lighter over all with distance. Value is the relative lightness or darkness of something, regardless of its hue. Pure black and pure white objects both look grayer at a distance. Very distant objects look very light in value because very few light rays from those objects are reaching your eyes, and those rays are mixed up with rays from the light value sky.
Distance lowers intensity as well. Intensity is the relative purity or brightness of color. Intense colors are composed of a relatively narrow band of light wavelengths. Distance dulls their intensity by broadening the band–scattering some of the pure hue light rays and blending in other colors from the landscape. The effect is similar to neutralizing a bright color such as cadmium orange by adding its complement, ultramarine blue.