"There is a kind of perspective called aerial perspective which depends on the thickness of the air. " Leonardo da Vinci
 

The planet earth is often called the 'blue planet' because of the blue oceans that are so apparent from space. Our sky is blue and our oceans appear blue from space. It is molecules in the air scattering blue light from the sun that is the reason we see blue.

Distant mountains are blue for much the same reason. We live under a thick layer of atmosphere that is not clear. There are tiny water droplets in mists and humidity. In dry climates there is often dust, polutants or other particles in the air. All affect the way we see objects at a distance.

The actual (local) color of an object, a mountain rock for instance, will seem different at a distance in value, hue and intensity.
 

The fact that far mountains are paler in value than near rocks seems obvious as layers of hills become progressively lighter into the distance. There is also a difference in contrasting values. The near landscape rocks are sharply lit with strong contrast of highlight and shadow. In the distance the contrast between highlight and shadow is less pronounced.

A dark rock or mountain will be bluer (cooler) and lighter as we see through the obscuring particles. Lighter rocks or distant buildings will be a little warmer in color and somewhat darker.
 

The warmer colors of reds and yellows will lose some of their intensity at a distance. Bright red and yellow autumn trees nearby will be less colorful on a distant mountainside as the hues become more neutral. Reds and oranges will lose their color faster than the cooler blues and greens.

While it is usual to perceive atmospheric perspective as affecting the color of objects at a great distance, the same principles hold true in closer proximity. The eye reads the colors in a painting to 'see' a scene or still life. Even the arrangement of fruit on a tabletop needs a lighter, more blue (cool) and more neutral background to be understood as having a sense of depth.

As you paint, study your subject, whether landscape or still life.  Look for the bluer (cooler) background to help give it "atmospheric perspective".

By Sharon Himes
Information supplied by: http://www.worldofwatercolor.com