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Orange is Tertiary:
The Theory of Colour


New translation, the Magna Carta

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Seeing colour
Naming colours
Some other comments and interesting 'facts'


The picture below is a prettified form of colour wheel. It illustrates primary, secondary, tertiary and quaternary colours in an aesthetic setting. The colours in this colour wheel are based on the actual responses of the eye to colour.

The construction is referred to as a Super Tangram (for which patent is pending). The idea is derived from a simpler form, the tangram, which is known in China as the seven board of wisdom or cunning.


       Hover your mouse pointer over a colour to see its name
1 Red
2 Coral
3 Orange
4 Tangerine
5 Yellow
6 Peridot
7 Lime
8 Apple
9 Green
10 Leaf
11 Aquamarine
12 Turquoise
13 Cyan
14 Sky
15 Cobalt Blue
16 Indigo
17 Blue-violet
18 Plum
19 Purple
20 Mallow
21 Magenta
22 Rhodium
23 Raspberry
24 Mulberry
Tangram 17: Colour Wheel, 1994/Acrylic on 9mm plywood, 90 x 90 cm. © abelard, 1998 1 red 2 coral 3 orange 4 tangerine 5 yellow 6 peridot lime 8 apple 9 green 10 leaf 11 aquamarine 12 turquoise 13 cyan 14 sky cobalt blue 16 indigo 17 blue-violet 18 plum 19 purple 20 mallow 21 magenta 22 rhodium 23 raspberry 24 mulberry
  Tangram 17: Colour Wheel, 1994
Acrylic on 9mm plywood, 90 x 90 cm
© abelard, 1998, all rights reserved

A new basis for teaching and understanding colour in a standardised manner has been developed. It can be used in schools and elsewhere.

The teaching of colour has developed haphazardly and is based on the effects of mixing (poorly defined) pigment colours. When these given pigments are mixed together, the effect is to reduce the colour strength of the individual pigments in the mixture, hence the term 'subtractive colour'. This is extremely confusing especially to a child, who comes to think in terms of adding colours together to achieves a result that is, in reality, less colourful. This less colourful result is rarely hinted at, let alone specified.

It is better that the child is first taught in terms of adding colour by projected lights and then explaining clearly the negative effects of mixing pigments. A widely accessible source of projected light are stained glass windowsback to contents


pretty dividing line showing the visible spectrum

Seeing colour

The human eye has four types of light receptors:

the rods which are sensitive only to black, white and shades of grey, and
the cones of which there are three types, each of which responds to a different range of colour.[1a]

The rod receptors are less precise than the cone receptors in their information-collecting ability for small changes, for example in edge detection, and they respond only to light and dark. However, rods have the quality of responding to a very much lower light level than cones and are the only receptors which function at low light levels.

Should you move from a lighted area to the light level at which the cones do not function, you will be blinded temporarily. The rods will start adapting to the lower levels of light available within a few minutes. You will develop a considerable amount of vision, because of the rod's low-light response ability. Most of this adaptation occurs within five to seven minutes, but it can continue for up to an hour. At these levels of light you will no longer be able to see colours (because the cones are not working) and, because of the lower precision of the rods relative to the cones, edges will be markedly less clear or precise.

The other three types of receptors are called cones. At low light levels, cones cease to function.




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Cones respond to different wavelengths of light, as follows:


graph showing cone reponses to light - three curves

nm=nanometre; 1m=109nm

This diagram shows that there is a degree of overlap between the response of the types of cones.

Also, you can see from the diagram, the blue-violet cones are less sensitive to light. Approximately twice as much light (quanta) is required to obtain from the blue-violet cones a perceived light level that is similar to that obtained from the red and green cones. Or, in other words, full response of the blue-violet cones requires more light energy than for the red or green cones. Thus, at a given light level blue-violet appears darker than red or green. This relative darkness applies also to mixes involving the various cones (colours), hence the natural brightness of yellow which stimulates the two most reactive sets of cones in the eye.

Another interesting factor is that the eye has a hard job focusing all three colours at the same time. Focusing is particularly difficult with blue-violet and this results in the haze effect caused by blue-violet light which can lead to headaches. These headaches can be relieved by using yellow-lensed sunglasses that filter out the blue-violet light.
The eye is generally more sensitive in the mid-ranges around 520nm, with its sensitivity tailing off in both directions.

Further study of the cone response diagram will show that there is some overlap of cone response. This is especially worth noting in the blue-violet area where the red cones fire in certain wavelengths. Thus we see (perceive) redness in that area of the blue-violet region and we see true blues as if they have some red added, these colours being commonly called violets. As this effect drops off, it is possible that you may see a magenta effect on both sides of a more 'bluish' area of the colour wheel

Red, green and blue-violet are regarded as the three primary colours of light. They stimulate one cone type and the brain translates this information received by the eye into what we call colour. When two sets of cones are fired, we respond that we see for instance yellow - a mixture of red and green light. The primary colours can be seen in the spectrum or rainbow, red at one end, green in the middle and blue-violet at the other end. In between these colours may be seen secondary colours that are, perceptually, each a mixture of two of the primaries.

Thus, you will see yellow between red and green, and cyan blue between green and blue-violet. The third secondary colour of light is magenta. This is not part of the spectrum, it has no single wavelength of light, but the sensation of magenta may be perceived by looking at a combination of red and blue-violet light. (It can be distinguished between the two parts of a double rainbow). It is interesting to notice that, with the wavelengths yellow and cyan our eyes decompose the light into responses made by two cones, then our brains recombine them into the sensation of yellow or cyan. That is, we never directly perceive yellow or cyan.

A rainbow may be seen by viewing light through a simple prism. Isaac Newton named seven colours for his spectrum - red, orange, yellow, green, blue, indigo, violet. One does not really see indigo as a separate colour, and orange is a bit doubtful. Newton came from a culture where specific numbers were regarded as having mystical significance, so he added the names orange and indigo to make the magic number seven.

The secondary colours (yellow, cyan and magenta) appear brighter because two sets of cones are firing together. These secondary colours are the basic colours of  colour mixing for painting. However, our children are taught crudely that the mixing colours are red, yellow and blue. This leads to much confusion later if they become interested in colour work.

To add to the confusion, different people are taught to match particular colour-names to different colours. This is particularly true of the blue area. It is sensible to exercise care when teaching these mixing colours.

 Colour printing does not rely on colour mixing, but on very small dots which are so close to each other that the eye sees them as a continuous colour. The dots can be seen through a small magnifying glass.

Tertiary colours are also shown in the picture. These colours are a mixture of a primary and a secondary colour. Thus, red (a primary) and yellow (a secondary), when combined, are seen as orange.

Conversely, it becomes clear that a green effect can be obtained either by mixing yellow and cyan pigments or from a single green back to contents pigment and in similar mode for reds. Of course, all magenta pigments are mixes of two pigments.

Naming colours

I have named the tertiary colours as follows:

  raspberry aquamarine  
  purple lime  
  cobalt orange  

There are also quaternary colours shown, they are a mixture of a tertiary colour and either the primary or secondary colour closest to that tertiary colour in the colour wheel. Thus there are twelve quaternary colours.

The complete list of my names for the colours is as follows:

  colour 1 "Red" (primary) colour 13 "Cyan" (secondary)  
  colour 2 "Coral" (quaternary) colour 14 "Sky" (quaternary)  
  colour 3 "Orange" (tertiary) colour 15 "Cobalt Blue" (tertiary)  
  colour 4 "Tangerine" (quaternary) colour 16 "Indigo" (quaternary)  
  colour 5 "Yellow" (secondary) colour 17 "Blue-violet" (primary)  
  colour 6 "Peridot" (quaternary colour 18 "Plum" (quaternary)  
  colour 7 "Lime" (tertiary) colour 19 "Purple" (tertiary)  
  colour 8 "Apple" (quaternary) colour 20 "Mallow" (quaternary)  
  colour 9 "Green" (primary) colour 21 "Magenta" (secondary)  
  colour 10 "Leaf" (quaternary) colour 22 "Rhodium" (quaternary)  
  colour 11 "Aquamarine" (tertiary colour 23"Raspberry" (tertiary)  
  colour 12 "Turquoise" (quaternary colour 24 "Mulberry" (quaternary)  

Much teaching about colour in art is exceedingly 'sloppy' and one is taught to regard and refer to pale and dark colours.

Colours are not pale or dark as such, colours are just colours. The various palenesses and darknesses which we observe are the (due) result of either of two phenomena. The first is the general (ambient) light levels in our surroundings. The second is, in the case of paint mixing, the 'pollution' of the 'coloured' medium that we are using by other particles of varying reflectivity, pollutants such as carbon or ground glass. The mixture's reflectivity is thus altered.

From the foregoing, you will gather that similar effects may be achieved by either pigment pollution or changes in ambient light.back to contents A colour mix, as previously discussed, may also be thought of as a mutual pollution of each of the colours in the mix.

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pretty dividing line showing the visible spectrum

Some other comments and interesting 'facts'

1a Information on the evolution of colour vision is available here.
Information on the evolution of different kinds of eyes, see chapter 7 of
Dawkins, Richard,   Climbing Mount Improbable
$13.45 [] {advert} 1997; W.W. Norton & Company; 0393316823; pbk
£7.19 [] {advert} 1997; Penguin Books; 0140179186; pbk

Two special states of visual response we perceive as black and as white. Black is, in fact, a total absence of light, whereas white is an effective complete over-loading of the visual system where all receptors fire at once and so distinctions cannot be made any more than in blackness. Such a state is rather akin to the state referred to as 'noise' (white noise!) in various contexts.

related material
butterfly black

“....In 2002 he unveiled 'Super Black', a pitted nickel-phosphorus alloy coating that achieves a similar effect to the scales of P. ulysses.

“Super Black will be most useful in the construction of optical instruments, Brown predicts. "But we've also had interest from artists who are not satisfied with the blackness of their paints," he adds.”

2 It may be of passing interest to note that the visual part of the brain is at the very rear of the head and that the right eye sends its messages to the left part of the brain and visa versa. The receptive surface at the back of the eye (retina) is in effect an exposed surface of the brain.
3 Some colours such as yellow form a single wavelength in the spectrum. However, when we look at yellow, two receptors of the eye are fired - red and green. The signals from these cones are recombined in the brain to give us the experience of yellow. Therefore, it is not possible for our perceptual system to distinguish whether we are looking at yellow formed by a single wavelength or a judicious mixture of red and green wavelengths.

The magenta area (the colours between red and blue-violet) has no such single wavelength in nature and so is always mixtures of wavelengths. Mixed wavelength and single wavelength colours may be distinguished by a selective use of filters. For example, viewing magenta through a yellow filter will block blue-violet light and then you will be able to see clearly the red component; that is, the magenta will appear red. Likewise, viewing the magenta through a cyan filter will block the red component leaving the blue-violet component visible.

4 By the use of colourants and pollutants and of texture, surfaces may be constructed so that they change in various light conditions, thus adding interest to a painting. For instance, variations in the height of paint throw tiny shadows according to the position of the light source and so change as the light source moves. Keep in mind that light does not just reflect from the surfaces of paint, but penetrates the paint and bounces around. Hence the substrate layers of paint are not entirely neutral, this is part of the relevance of priming surfaces with white or other substrates.
5 A particularly interesting part of the spectrum is in the region of blue-violet where, strangely, the red cones also fire, making the human 'see' red in the short-wave (blue) visual light. The amount of red perceived and just how far into the short-wave light the individual sees will vary from person to person because of natural human variation.

It is even possible that this red effect increases then decreases towards the extremes of perception leaving a reddened hill with blue-violet either side. As the red component increases when moving into the magentas, the effect of this edge or wrap-over area of light seems to allow an extra number of quite clearly distinguished and subtle colours in this special region of the colour circle. Also refer to the cone response diagram.

6 I have incorporated the relative darkness into the colours which I use as standard to give a better feel for the realities of colour, rather than brightening all the colours up by the addition of white (e.g. ground glass).
7 'Flat' colours tend towards a degree of 'deadness'. Variation in surface and paint textures are part of the craft of painting and they can be deliberately manipulated. Painting is a craft skill. How effectively you achieve results that you wish will depend upon understanding the materials you manipulate. In all teaching and learning it is necessary to give both the theoretical information, such as that discussed in this paper, and to make viable real world experience - one without the other tends to poor teaching and poor learning. For example, it is important that learners gain real world experience of going from bright light conditions into darkened ones.
8 Information on colour generally is not available from one source. The knowledge is scattered amongst documents about biology, physics, art and chemistry.
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pretty dividing line showing the visible spectrum

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