Thinking about colour • 1

In feedback after assignment 4, my tutor commented:

You have clearly observed and recorded colour in the work and created your own colour palette. In relation to this I would like to have seen further development with research into theory and symbolism in the use of colour.

I therefore plan a series of three postings, between now and the end of the course, dealing with colour. As Itten(1974) has pointed out, there are many ways of looking at colour: a physicist will be interested in radiation and optics, a chemist in the nature of pigments and paints, a painter in the way that colours interact on the canvas etc.

This first posting, dealing loosely with the scientific background, will be mostly unreferenced because the starting point is high school physics lessons and other influences too deeply ingrained to unravel.

What colour is

Visible light is one manifestation of electromagnetic radiation. The full spectrum ranges from radio at one end to gamma radiation at the other, a total of 400 octaves of frequency (Asimov ‘Four hundred octaves’ a 1982 essay collected in Asimov 1984). Of this, slightly less than one octave (approximate wavelengths between 400 and 700 nanometers(frequency 430-750THz)) is visible to the human eye. The phenomenon that we call colour is the brain’s way of interpreting the difference between frequencies of visible light.

1210px-linear_visible_spectrum-svg

source: Wikipedia

These colours can be seen in natural phenomena such as rainbows, but it was only when Isaac Newton demonstrated splitting and recombining the colours from white light with a prism that the principle was understood. The spectrum above also shows the invisible radiation at either end of the visible range, infra-red and ultra-violet, which can also be recorded by cameras. The naming of the traditional seven colours has more to do with mysticism than science: indigo is really a dark blue and there are no discrete colours in a continuum.

The (in my opinion) questionable next step is to turn the linear spectrum into a ‘colour wheel’ by stitching the red and blue ends together through a range of colours known variously as purple, magenta or mauve. I suspect the reason why these colours are difficult to describe is that they are conceptually artificial.

The 1990 Schiffman diagram is the most ‘honest’ of these examples as it shows the pink-purple sector is separate from the ‘rainbow colours’. It also introduces the concept of saturation. However, whatever the scientific basis, the full colour wheel can be justified because it ‘works’ for colour mixing.

Primary and secondary colours

Although colours have almost-infinite variety, it is not necessary to have an enormous number of colour sources to reproduce them.

It is notionally possible to select a smaller number of ‘pure’ colours and mix the others from them. How many colours, and which, will depend on personal choice, the nature of the medium and the way in which the primaries are mixed. Usually, three primaries are used. Artists mixing paint, and schoolchildren using crayons, use red, yellow and blue as seen in the first diagram below.

The standard when mixing lights, and on colour TV screens, computer monitors etc. is to use red, green and blue, as illustrated in the middle diagram. This type of mixing is called additive because the lights are added to each other, the secondary colours (formed by mixing equal amounts of two primaries) are lighter and it is possible to produce white by mixing all three equally.

When printing, including computer inkjet and laser printers, the inks lie on the white paper and subtract some colours from the white base. Adding further ink reduces the colour still further and this type of mixing is called subtractive. The subtractive primaries are the same as the additive secondaries (cyan, magenta and yellow), producing red, blue and green when mixing in pairs and, notionally, black when they are all mixed together. In practice, a mixture of the three pigments is a rather muddy, dark colour rather than pure black, so printers will add a black ink to the set, giving the standard CMYK (Cyan, Magenta, Yellow, blacK) inkset of low-end printers. Because of technical issues in the way the inks are formulated and applied, the colour mixing of the basic four colours is not perfect, and high-end printers use additional colours to fill the perceived gaps. For instance, my Canon PixmaPro 9500 uses ten inks in nine colours: the basic CMYK set, lighter versions of magenta, cyan and black, plus red and green. There are two different blacks (matt black MBK and photo black PBK) but this is about ‘glossiness’ rather than colour.

Colour temperature

The colour of a scene depends on the colour of the light illuminating it. The eye and brain will accommodate this, to some extent and perceive the scene in its ‘true colours’. The process of ‘colour correction’ is an attempt to alter the true colour of the scene to accord with the way it is perceived.

The main reason for colour variation is the temperature of the light source. A physical concept called ‘black body radiation’ says that the amount of radiation emitted by a body increases with its temperature, and also that the average colour (peak of the frequency curve) tends toward the higher-frequency, short-wavelength blue end of the spectrum.

600px-black_body-svg

source: Wikipedia

Thus, the sun with its surface temperature of about 6000K emits light that we perceive as white (that being what the eye has evolved to do) but an incandescent light bulb, with a coil temperature of 3000K emits mainly infra-red (heat) radiation plus some visible light at the red/yellow end of the spectrum. The situation is more complicated with fluorescent sources, which have a discontinuous spectrum and require correcting on the green-magenta axis as well as the blue-yellow axis.

One curiosity is that the bluer colours are considered ‘cooler’, while red and yellow light is considered ‘warmer’ and more comforting, in contradiction to their relative physical colour temperatures. Partly, this is due to common experience; fire is yellow, ice is bluish. However, I speculate that part of the cause relates to Rayleigh scattering, by which the red-yellow light from the sun reaches us directly, while blue light is scattered and turns the entire sky dome blue. This means that an outdoor scene effectively has mixed light sources. Objects directly lit by the sun have a yellow tint while objects in shadow are lit by light from the sky dome and acquire a blue tint.

The next posting of the set will look at the way colours are used together, whether harmonious, complementary or ‘clashing’.

The final posting will look at some of the symbolism of colours.

References

Asimov, I. (1984) X stands for unknown. New York, NY, United States: Bantam Doubleday Dell Publishing Group

Itten, J. (1974) The art of color: The subjective experience and objective rationale of color. 2nd edn. New York: Wiley, John & Sons

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