Here on planet Earth, we have a little thing called atmosphere, which makes it possible for us to stay alive. It also makes things look fuzzier the further away they are. If it is night-time, things will probably look darker if they're farther from you. If the sky is a light gray, mountains and buildings may look lighter and softer from far away. Atmospheric perspective is a way for artists to show depth in their paintings.
Before mixing paint, students had to research and draw landscapes or cityscapes, thinking about vertical placement of rooftops or mountains. The foreground is at the bottom of the paper, the sky is at the top, and there are several divisions in the middle.
The color, straight out of the bottle was used to paint the middle ground before tinting and shading in increments for the other layers. My students who were completely blind decided what they wanted to paint and what color to use. Then I cut out layers of cardboard and paper for them to paint on their own. Ultimately, we glued the layers together. This makes for a tidier end product for sighted students as well.