Rather, it is in the supposition that colors lie in the observer and not outside him. The brain is only interested in obtaining knowledge about those permanent, essential or characteristic properties of objects and surfaces that allows it to categorize them. But the information reaching the brain from these surfaces and objects is in continual flux. An object may have to be categorized according to color, as when judging the state of ripeness of an edible fruit. The ability of the brain to assign a constant color to a surface or a constant form to an object is generally referred to as color or object constancy.
Perceptual constancy is a much wider phenomenon.
It applies as well, for example, to faces that are recognizable when viewed from different angles and regardless of the expression worn. There is also what we can call situational constancy, when the brain is able to categorize an event or a situation as a festive or a sad one, and so on, regardless of the particular event. There is narrative constancy when, for example, the brain is able to identify a scene as the Descent from the Cross , regardless of variations in detail or the style of the painting. It is a general scene of mourning. The scene has been gradually extended by artists, but it is always recognizable.