Atmospheric Perspective: Giving the appearance of distance by the use of colour and tone, quite often by making distant subjects paler, less saturated with colour and with less distinct outlines.
You do not always have to fade to blue, although this is probably how it is most commonly seen. As this demonstration shows, other colours will work.
In these examples no other useful devices are used give the impression of distance. There are no converging rail lines; no carefully placed people or lampposts of ever decreasing size. The only device we have to show distance is the depletion of colour, tone and definition.
To show greater distance, this could be pushed still further, until the horizon becomes a blur.
Where to see examples
Lots in the British watercolour tradition and Turner makes use of it exquisitely. That landscape in the background of Leonardo’s Mona Lisa…to give it distance... so it did not overpower the portrait… Leonardo used atmospheric perspective.
Just a note
Atmospheric Perspective is often mistakenly called Aerial Perspective. An Aerial Landscape is something else…that's the painting you will do when you’re in a hot air balloon!
How it's done: four examples
A quick study using blue shades. Painted in acrylic paint on acrylic paper.
The white paper was first tinted with a pale pink. For this I used a very thin wash of magenta. This was allowed to dry before painting on top. For speed I used just one brush; a soft, flat square ended brush. Pale cerulean blue was used for distant colours and phthalo blue (phtalocyanine blue) to achieve the darker tones of the foreground. For the very dark colours mix the phthalo blue and burnt sienna together, this will make a very dark colour (an uneven mix will help give a greater variety of colours), keep some on the side of your palette. Add some of this mix to your phthalo blue to achieve increasingly darker shades. You should get a near black.
Similar to study 3, but overlaid with a thin wash of titanium white
Using the same magenta tinted paper as the first example, but this time using a palette of magenta with varying amounts of white, painted a little thicker than before to allow it to be seen on the lightly tinted paper. As in the example above, mix some phthalo blue and burnt sienna together to make a very dark colour, (again an uneven mix will help give a greater variety of colours). Keep some of this new colour on the side of your pallette. Add some of this mix to your magenta to achieve increasingly darker shades. Again it is possible to reach a near black.
This was painted exactly as above but with a rich orange/yellow in place of magenta. The same mix of phthalo blue and burnt sienna was used to darken the colours in the foreground.