Colour is an event because it requires the participation of three components at a particular point in time to take place. In addition to the object, we require a light source and an observer. Only with the interaction of these three things — object, light, and observer — can we have a colour event or experience.

“If we see someone wearing a yellow sweater illuminated by a bluish cast of light, we still ‘see’ a yellow sweater, even though we have no trouble identifying the colour in the sweater as green if it is isolated from the scene.”

We need some help from three branches of science, physics, physiology and psychology, to understand how the object, light, and observer contribute to the colour event. If you like memory aids, you can use the acronym POLO to remind you of the three science P’s and the object, light, and observer.

Object

The object and light fall under the domain of physics, while we need both physiology and psychology to describe the observer’s role in the colour event.

The object’s role is to interact with light, and the object can either reflect light back from its surface or transmit light through itself. Reflectance and transmission are the two potential interactions. The majority of objects are opaque, so most of the time we are dealing with the reflection of light.

If an object is semi-opaque, and transmits a portion of light, we refer to it as translucent.

Light

Visible light is a tiny sliver of the total electromagnetic spectrum. The electromagnetic spectrum contains all forms of energy, ranging from kilometre-long radio waves at one end and progressing in shortening wavelengths down through microwaves, infrared waves, ultraviolet waves, X-rays, and finally, gamma waves with wavelengths of a subatomic dimension

The greatest complexity of the colour event occurs in the interaction with the observer. The science of physiology, the study of the human body’s functions, provides half the story. Psychology, which provides insights about the function of the mind, completes the tale.

The effect of colour constancy provides a very important lesson in judging our success in colour matching: it is more important to preserve the overall colour relationships in our image than to focus on individual colour accuracy.

In our mind’s eye, not all colours are created equal. Due to their historical importance to our survival, we pay special attention to certain colours. Flesh tones, the blue of the sky, and the greens of grass are known as memory colours due to the additional weight they have in our hierarchy of colour.