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What is colour?

The term colour refers to a sensory impression that is created when our eyes and brain attempt to process radiated or reflected light. Light itself is a type of energy that behaves as a wave, and without it there could be no such thing as colour. White light is actually composed of many different colours of light, each of which can be identified according to their wavelength. The various colours of light that the human eye is capable of detecting are referred to as the visible spectrum of light. At one end of the visible spectrum are the short wavelengths of light we perceive as blue. At the other end are the longer wavelengths of light we perceive as red. All of the other colours we can see are found somewhere within this spectrum.

Colour theory

In order to reproduce any of the colours in the visible spectrum of light, we must employ one of two colour theory systems. The first system, known as an additive colour system, is used by devices that are capable of emitting their own light, such as computer monitors or televisions. The second colour system, known as a subtractive system, creates the appearance of colour by reflecting and absorbing ambient light. This is the type of colour system that is used in printing processes.

Additive Colour Theory (RGB)

In an additive colour system, red, green and blue light combine to create white light. The key feature of this system is that we see the colour because it is being emitted by the source. In this colour scheme, black is created by the absence of light. Combining all three primary colours creates white light. The most common example of an additive colour system is a computer monitor.

A subtractive colour scheme is slightly more complicated. In this system, cyan, magenta, and yellow inks subtract colours from white light and combine to create black. The key feature of this system is that we see the colours because light around us (from the sun or a lamp) is reflected off the surface of something (such as paper). In a subtractive system, we start with the white light reflected by the surface of the paper and use printing inks to remove certain colours. It works like this: paper appears white because it reflects red, green and blue light in mostly equal proportions (which will combine to make white light). Printing inks are designed to act as light filters; that is to say that if we were to apply a layer of cyan ink to a sheet, what we would actually be doing is preventing red light from being reflected off the surface of the paper. This is important to note, because when the red component of white light is removed, only green and blue are left, and these two colours combine to create cyan light. Each of the three primary colours in this scheme will absorb a certain colour of light:

– Cyan: absorbs red, and reflects blue and green

– Magenta: absorbs green, and reflects red and blue

– Yellow: absorbs blue, and reflects red and green

Early on, printers realized that if you print cyan, magenta and yellow on top of one another, the colour you end up with is much closer to muddy brown than black. This is because the pigments used to give ink its colour are imperfect, and even under ideal conditions will not block 100 percent of any colour. As a result of this shortcoming, black ink was added to the the subtractive colour system we use in colour printing processes.

Conclusion

Colour theory is important because it has such far reaching implications for the graphic arts industry. For the average person, it can be easy to forget how complex a subject it can be; physics, the physiology of human vision, psychological factors, and even cultural influences can affect how a viewer perceives colour. However, as colour is very much a part of our business it is in our interest to understand the factors that influence how it is reproduced.