How we see
When light enters the normal eye it is focused on the retina by the eye-lens. The retina is coated with a material called 'visual purple', in which are embedded the rods and cones at the nerve ends. According to one theory, when light falls upon the visual purple, a photoelectric action takes place, and electrons are freed as they are in a photoelectric cell. These freed electrons set up currents in the visual purple which are detected by the rods and cones. These in turn set up currents in the nerves that carry them to the brain and produce the sensation of sight. The exact action in the brain is still unknown. The nerves are the circuits that carry the message to the brain. The eye interprets different wavelengths or frequencies as colour. Notice the remarkable similarity between this system and an ordinary vacuum tube radio receiver with its tuning circuits.
Seeing colour
The apparatus we use to perceive colour is a three-dimensional system. In bright light, the eye uses three types of detector (cones) in the retina. Each type has photochemical pigment whose peak sensitivities are tuned respectively to the long, middle and short wavelengths of the spectrum. The eye registers three separate bits of information which are then weighed and combined to produce our final sensation of colour. The rods perceive light and dark. It is also believed that various sections of the visual purple are receptive to specific visual features such as vertical lines, horizontal lines, diagonal lines etc.
Light is a form of radiant energy which travels in waves and is part of the electromagnetic energy spectrum. This energy is measured in wavelengths or frequencies and these determine the colour of the light. Wavelengths are measured in millimicrons (1mµ = 1/1,000,000 mm) and frequencies in cycles per second (cps). Light is thought of as consisting of both waves and particles (photons).
The lightwaves themselves are not coloured. Colour is the experience by a receptor (us, for example) of the absorption or reflection of light. We have evolved to respond to only a part of the spectrum of lightwaves emitted by the sun. The human eye is capable of perceiving only a portion of the Electromagnetic Energy spectrum between 400 and 700 millimicrons or roughly from red to violet.
Much of the sun's radiant energy is absorbed by ozone and water vapor in the atmosphere. The sun's most intense emissions are in the blue-green part of the spectrum; however these colours (along with indigo), have short wavelengths which are most affected by the scattering effect of molecules (e.g. water) in the atmosphere. The scattered blue lightwaves/photons is what makes the sky look blue. Because most of these wavelengths do not reach our eyes but longer ones do, the sun looks yellow. If we look towards the setting sun we receive the long-wavelengths that are usually scattered least getting to our eyes. Dramatic red and orange sunsets happen over the most polluted cities or after volcanic eruptions or vast fires because they are caused by a superabundance of scattering particles in the atmosphere which disrupt even long wavelength light. When the scattering particles are bigger (e.g. raindroplets, snowflakes, sand or dust) then the scattering ceases to depend significantly upon wavelength and all the wavelengths are scattered more or less uniformly so that we see a misty or monotone scene. This is why clouds and overcast days appear white or gray. There are even some animals that use light interference rather than pigmentation to look white: the polar bear, for example, has transparent hairs which contain tiny bubbles of air which scatter the light so that it appears to be white. (The colours in a peacock's tail are also caused by scattering light and the consequent interference patterns but it uses metallic pigment bubbles in its feathers to do it).
Moonlight is just reflected sunlight so has a very similar spectrum to direct sunlight but its intensity is about a million times less. Starlight is about a thousand time less intense still.
Twilight, as mentioned, changes the perceivable spectrum slightly. When the sun is low in the sky its light must pass through more of the atmosphere before reaching us and the red through to yellow wavelengths become more scattered. This leads a clear sky to appear pink or apricot-coloured. Some scientists have hypothesized that this twilight colour-shift has given rise to important evolutionary adaptations in humans. One evening in 1819, Jan Purkinje, a Czech physiologist, was sitting in his garden when he realised that that the relative brightness of different coloured flowers were changing as the light faded; red quickly became black whilst blue flowers and green leaves remained bright and colourful. This is because the human eye becomes more sensitive to blue and green light in low-light situations. This seems strange insofar as we know that the daylight (not to mention moon and starlight) that reaches our eyes contains more long (red and yellow) wavelengths. Purkinje theorised that this was because twilight was the most dangerous period for our ancestors; it's when predators wake up hungry and on the hunt whilst humans are usually at their lowest ebb. Evolutionarily, it is more effective to beef-up perception in the green-blue spectrum and have better vision during a brief but dangerous period of the day than to optomise night-colour when the levels of light are too low to be of any real use.
When white light passes through a prism it is dispersed into the spectral colours. If this dispersed ray of light is projected onto a surface the spectrum will be displayed. The prismatic spectrum is a continuous band of colour ranging from red through orange, yellow, green, blue, to violet. The wavelengths and frequencies of these colours are listed below:
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Light with a wavelength more than 700mµ falls into the infra-red spectrum and light with a wavelength less than 400mµ falls into the ultra-violet spectrum. These wavelengths are invisible to the human eye (but not to some animals) as are gamma rays, x-rays and radio waves. If this spectrum were to be recombined through a converging lens the result would be white light.
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Primary colours are those which cannot be produced through the mixing of of other colours. We deal with three sets of primary colours:
Additive primaries - Red, Blue & Green Subtractive primaries - Red, Blue & Yellow Process colours - Cyan, Magenta & Yellow (plus Black) Additive colours are produced by radiant sources such as the sun. When the three additive primaries are mixed together they produce white. Each primary represents a third (almost) of the spectrum, thus as you add another primary more of the spectrum is present. When all three primaries are added the entire (almost) spectrum is present in the form of white light. A large section of the visible spectrum can be produced by mixing these primaries in varying amounts. They are used in theatrical lighting, videos, film recorders and tv/computer monitors. |
Subtractive colours are produced by pigments. Each subtractive primary works as a filter absorbing all light shone upon it except for its section of the spectrum which it reflects. Therefore as another primary is added less light is reflected. When all three primaries are mixed the result is an absence of light - black. Subtractive primaries are used in painting, drawing, dyeing etc.
Process colours are subtractive colours. When Cyan, Magenta & Yellow are mixed the result is a muddy brown thus Black is added as a fourth primary to give proper blacks and for use in type. They are used in printing.
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Secondary colours are produced when any two of the primary colours are mixed. Additive primaries secondary colours Red + Blue = Magenta / Blue + Green = Cyan / Green + Red = Yellow Subtractive primaries secondary colours Red + Blue = Violet / Blue + Yellow = Green / Yellow + Red = Orange Process primaries secondary colours Cyan + Magenta = Blue / Magenta + Yellow = Red / Yellow + Cyan = Green Tertiary Colours are a mixture of two secondary colours. Complimentary Colours are colours that are placed opposite each other on the colour wheel Analogous Colours are colours that are placed next to each other on the colour wheel. |
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What use is colour?
"Colour is a power which directly influences the soul. Colour is the keyboard, the eyes are the hammers, the soul is the piano with many strings. The artist is the band that plays, touching one key or another to cause vibrations in the soul"
Wassily KandinskyFour adaptive uses of colour in nature have been identified:
- To attract attention: e.g. coloured fruit signal that they are good to eat; flowers signal their presence to insects.
- To warn: e.g. luridly coloured reptiles and insects signal that they are poisonous
- Camouflage and mimicry (see above)
- To stimulate the emotions: e.g. some animals use colour to signal that they are available for mating and are better than their peers (see human use of cosmetics, for example).
We continue to be affected by and use colours in ways that reflect these evolutionary biological purposes and responses. In design contexts colour is a central component of communicating information on both a conscious and unconscious level.
Colour contains information: e.g. the green/amber/red succession is now so deeply embedded in contemporary culture that its use is always read as stop/wait/go. Maps often display colour scheme that make them easier to read and understand -- colour areas of water blue, shading landforms in tones of green and brown to indicate topographical features etc.
Colour is used to draw attention to important information; bright or highly contrasting colours draw the eye more quickly than subtle and low-contrast palettes.
Certain colour schemes are used to appeal to particular audiences, to create a particular mood or to denote particular values; e.g the use of green and brown hues are used to connote that a product is environmentally-friendly, natural etc.: pastels and flowery shades that a product is soft, comfortable and unthreatening.
Colour helps people to differentiate and remember information (hence the recent successful push by corporations to trademark specific colours). Obvious examples include the use of different colours to code wiring and pipes in industry: colour to define identity such as national flags, sports-teams uniforms.
Cultural and Individual Factors
Detailed studies of colour words and hues to which they respond show a virtually universal choice of parts of the spectrum to which colour words correspond with the principle cultural difference being the number of colours distinguished by colour words. The simplest languages had words for light and dark only, and then in order of specificity, red was generally added, followed by green and yellow in roughly equal frequency, then blue, followed by purple, pink, orange and gray. We continue to recognise the primary importance of black, white and red in ceremonial and communications contexts. Many languages have more words which describe shades and hues in specific parts of the spectrum. These tend to related to importance in the environment and culture; thus Inuits have more words that describe snow-colours than Trobiand Islanders who have more words that describe greens and browns.
Colour preferences also vary from culture to culture. In Western cultures most children nominate warm colours such as red,orange and pink as their favourites. As they get older their preferences change with most adults nominating blue or green. Adult Japanese people, by contrast, usually nominate black or white as their favourite colour.
Many cultures further designate some colours as being appropriate for one sex only; for example, until very recently, anglo cultures considered pink to be a feminine colour and blue a masculine colour. Men are still generally restricted to a far smaller palette of colours deemed appropriate for apparel, personal items and environments. Computers, for example, were ubiquitously gray or beige until recently. It wasn't until Apple saw that the lucrative female market was not being catered to and introduced a range of personal computers designed to appeal to them, that computers stopped being colour-coded as masculine and business-oriented (read beige and boring) and started being produced in a range of colours (and now, patterns).
In addition, there is a wide range of individual differences in colour perception.
- Older people are less sensitive to colour and often need higher brightness/contrast levels. They also lose the ability to discern blue hues.
- Eight percent of males and 0.5 percent of females have colour deficient vision. The most common deficiency is the inability to distinguish between red and green.
Colour Symbolism
Most cultures imbue certain colours with special significance, however the meanings of these colours varies from culture to culture. For example; we think of black as being the colour of death and mourning but Pacific Islanders associate and use white in these contexts. Most cultures, however, give special significance to red, but even within the same culture red can have oppositional meanings. In western cultures, for example, red signals both danger and sexuality.
Some colour symbolism is enshrined in our language:
- seeing red, red-tape
- green with envy
- yellow-backed/livered
- feeling blue
- brown-study
- purple prose
Environmental Factors
The appearance of a colour depends on the colours that immediately surround it, the colours in its general environment, ambient light and size, shape and placement.
References
The New Graphic Design School, Alan Swann, 1997 New Burlington Books, London
The Art of Colour, Johannes Itten,1973 Otto Maler Verlag Ravensburg, Germany
Light, Colour and Environment, Faber Birren, 1969, Reinhold Book Corporation
An Introduction to Digital Prepress, Richard Imbro, 1997, AGFA Educational Publishing, USA
A Digital Colour Primer, Tim Waterhouse http://www.digitalimagingmag.com/current/prime.html
The Artful Universe, John D. Barrow, Penguin, 1995
The Interaction of Colour, Josef Albers
Color Symbolism In Buddhist Art http://www.exoticindiaart.com/article/colors
Shiralee Sauland John Bleaney 2001
graphics by John BleaneySee also:
- Computer colour
by John Bleaney and Shiralee Saul- Auditory perception overview
- The 'Laws of Perception'
- Our senses and 'percieving'
edited from 'GAPS, MAPS AND PERCEPTION: WHAT HYPERTEXT READERS (DON'T) DO,' J. Yellowlees Douglas
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