9. The colour wheel and natural order

The colour wheel is based on two phenomena: the psychological curiosity, known as the negative afterimage; and the way colours arrange themselves, in their pure state, from light to dark - from yellow to violet. The Colour Wheel is also known as the Psychological Wheel, because it is based on the psycho-physiological phenomenon of the negative afterimages. This means that the colours connected by lines running through the centre of the wheel are the negative afterimages (or complementaries) of one another. The wheel is also based on the natural order of colours. The term 'natural order' means that, in their purest condition (no matter where they are encountered - in jewels, minerals, flower and feather - and assuming they are seen in a good, clear light), some hues are light in value, some medium and others dark. This natural scale is one that lends itself to a kind of artistic structural sense and to a modern colour grammar or syntax. Yellow, being the lightest of all colours is placed at the top of the wheel; violet being the darkest is placed at the bottom. All the other colours range between these two extremes, the cool colours taking their places along the left side and the warm colours along the right side. The cool colours, because they are contractive, lie nearer the centre; the warm colours, being expansive, lie farther from the centre - hence the warped wheel.

The primary hues occupy the larger circles, the secondary hues occupy the medium- sized ones and the tertiary hues occupy the small circles. Therefore, reading clockwise from violet, we have :

a. Ultramarine blue, b. Green-blue, d. Green, e. Green-yellow, f. Yellow, g. Orange-yellow, h. Orange, i. Orange-red, j, red, k. Crimson, l. purple, and m. Violet.

The Achromatic (or Grey) scale, to the right, has been contrived in such a parallel way, as closely as possible, the values of colours on both sides of the wheel from top to bottom. There are 12 values in all, making it possible to divide the scale into three registers: the dark register runs from
0 (black) to 3; the middle register runs from 4 to 7; and the light register form 8 to 11 (white).

Absolutely pure hues are encountered less often in nature than one would expect. When they are found, for example, in certain flowers and insects, in certain tropical fish, in bird plumage, moths and butterflies, in certain gem stones, in a rainbow or in a spectacular sunset, they do seem to conform to the natural scale of chromatic values. In a sunset, one sees a gradual movement of colour down the natural order, from golden yellow to orange, to red, to crimson, to a greyed violet-blue, and finally to nightfall. In autumn, the green leaves of trees first turn a singing yellow, then a kind of orange, to an assortment of reds, to crimson, and then, to a rich purple-brown.

Another way of describing this stepwise movement up and down both sides of the colour wheel - the warm side (the yellows and reds) or the cool blue-green and blue side - would be to say that colour manifests itself according to a set of values ranging from light (almost, but not quite, on par with pure white) to dark (close to the condition of black). Certain hues, such as violet and ultramarine blue, pertain to what we shall refer to as the dark register, to the bottom sector of the value scale; red and green, for instance, pertain to the middle register; yellow and orange-yellow pertain to the light register, to the upper end of the scale. Yellow assumes the position of the lightest hue, and violet that of the darkest, in their natural order. That pure yellow and pure violet are very close to being what are called complementaries, or natural opposites, is another factor accounted for in the wheel - the spokes running from one side through the centre of the wheel to another side indicate these contrasting pairs, based on their afterimages. This circular scale of colours parallels the achromatic scale or value scale that forms the trunk of Munsell's colour tree. That no hue, in its natural order, touches the extremes of the achromatic scale (the no-colour scale) is readily understood; pure yellow cannot be as light in value as pure white, and pure violet cannot be as dark as pure black (technically the absence of all colour, despite the fact that some artists and theories insist on calling black colour). The colour scale, the wheel, exists within this wider range of values, as it does within the far wider range of the electromagnetic spectrum. We must bear in mind that we are dealing here with pigments and the appearance of colour in pigments or colorants, not with coloured light, luminous colour, or prime radiance. (Prime radiance strikes the eye with far greater energy than colour given to us from any kind of surface; and, as was mentioned earlier, paint is a surface). Naturally, a special case must be made for light passing though coloured substances.