The color circle, as generally understood and widely used, is a diagram with a continuous sequence of hues arranged in the order of the spectrum. (The gap between spectral red and spectral violet is bridged with extra-spectral purples.) The color circle diagram is used as a guide to color mixing and color composition. It is also used in the classification of colors and is incorporated in all three-dimensional color order systems.
Very many color circle diagrams have been designed and published. The essential feature is that the diagram must represent the sequence of hues in correct order and in a continuum: reds, oranges, yellows, greens, blues, purples, reds, oranges, yellows, greens, etc. The number of separate hues in the sequence can vary as can the hues themselves that are selected for inclusion. The starting point for some color circles is a choice of so-called primary colors. Other circles are organized so that colors opposite to each other are, in some sense, complementary. Many color circles are also organized so that the degree of difference between neighboring colors in the sequence appears to be the same all round the circle.
The Variety of Color Circles
There is no single “correct” design for a color circle. Different circles have been constructed on different principles. They are not necessarily presented in color; in some the colors are simply identified by name. Color circles can be grouped in three broad categories: those that represent colors as something physical, those that represent colors as visual phenomena – what people see –, and those where the colors can be understood as either or both, physical and/or visual. In the first category the colors represent lights, paints, inks, or dyes, and the position of the colors in relationship to each other is generally determined by their physical properties or by the way that these lights, paints, inks, or dyes can be mixed to produce a large range of other colors. In the second category the colors are simply themselves and it is their appearance that determines how they are related in the circle. In the third category it may not be clear whether the colors are to be understood as physical or visual or both. It could be that the designers and users of such circles confuse the physical and the visual aspects of color. For an account of the way that the physical and visual aspects of color can be confused, see the entry on “Primary Colors” in this encyclopedia.
As color circles fall into different categories, and are constructed according to different principles, the relationship between colors can vary from circle to circle. This does not mean that the sequence of hues can vary – that must always be the same – but the distance between hues can vary. For example, it could be that two different circles have yellow in the 12:00 o’clock position, but red might be at 3:00 o’clock in one circle and at 4:00 o’clock in the other. The principles underlying the design of the color circles would have fixed the position of red in relation to yellow. Problems can arise when there is a mismatch between the intentions of the designer and the expectations of the user. A particular color circle can be criticized for not representing particular color relationships when it was never the intention that such relationships be embodied in the design.
Precursors to the Color Circle
The color circle, as defined above, was invented by Isaac Newton, whose color circle is illustrated in his book Opticks, first published in 1704 (see Fig. 4) [1, pp. 32–35]. Before Newton it was believed that there was a beginning and an end to the sequence of colors. Aristotle had claimed that all colors derived from mixtures of white and black which he placed at either end of a linear scale [2, pp. 31–32]. Aristotle’s prestige was so great that science was dominated by his ideas until the time of Galileo [3, p. 213]. Some circular color diagrams do predate Newton but they still reflect Aristotle’s ideas.
Claims have been made that this second Forsius diagram represents a sphere [7, p. 224]. If this is correct then the central horizontal line must be read as a circle seen from the side with red, yellow, green, and blue on the circumference and gray in the middle. Werner Spillmann has applied the principles of graphic projection to this interpretation and points out that it would mean that the hues are in the wrong order [8, p. 7]. Yellow must be closest to the observer and green farthest away or vice versa. Either way, the hue sequence would be red, yellow, blue, and green, which is not the order in which they appear in the spectrum. However these early diagrams are read, not one of them, unequivocally, shows the sequence of hues as continuous and in the correct order.
Development of the Color Circle
The color circle did not evolve so much as develop a growing variety of uses. Newton’s circle identifies colors with light of different wavelengths and he shows how the diagram can be used to illustrate the results of additive mixing. Some later circles illustrate the results of subtractive mixing from a set of “primaries.” In other circles the positions of the colors are determined by how they appear. Such arrangements are used in systems of color identification. Color circles have been developed where the apparent difference between neighboring colors is the same all round the circle. Colors that are opposite to each other in some circles are described as being complementary. Even spacing and complementary relationships are seen as significant in theories of color harmony.
Strictly speaking, the sequence of hues in Newton’s circle is incomplete. The circle is divided into seven segments, each identified by name. At first Newton refers to each segment as representing a single color – “Let the first part DE represent a red, the second EF orange …” – but he goes on to say that these represent “all the colors of uncompounded light gradually passing into one another as they do when made by Prisms …” [1, p. 32]. So the segment DE does not represent a single red but a range of the hues that would be identified as “red.” And the lines that separate the segments represent the borders where colors that would be identified by one name give way to those that would be identified by the next; the “red” segment would have a range of colors from reds to orange-reds. Because the colors in the circle represent the wavelengths of light in the visible spectrum, there is no place for the bluish reds and purples that are not visible in the spectrum. And if the hues shade into each other across the borders separating the other named segments, there would be a break in the sequence at point D with no spectral hues to shade from violets to reds.
The colors in Chevreul’s circle between the 5:00 o’clock and 7:00 o’clock positions are not visible in the spectrum and so have no place in Newton’s circle. However, if Newton had intended to represent seven hues only, with no shading from one named hue to the next, the gap between violet and red would be no more noticeable than that between red and orange. The hues are in the correct order and the sequence is continuous.
The First Color Circles Published in Color
Harris was an entomologist as well as an accomplished artist. Reference to his color circles would have been helpful when identifying and recording the colors of butterflies and other insects, while the circles could also serve as a guide to mixing paints to match those colors. Furthermore, Harris may have been the first to point out that a color circle can reveal relationships between colors that would now be called complementary. He refers to “contrasting colors” that are “so frequently necessary in painting” [11, p. 6] and goes on to explain how one should “look for the colour … in the system, and directly opposite to it you will find the contrast wanted” [11, p. 6]. And he provides a kind of definition: “if the colours so mixed are possest of all their powers, they then compose a deep black” [11, p. 7]. One current definition of complementary colors is that they should mix to a neutral – white from additive mixture in the case of lights, gray from partitive mixing in the case of colored segments on a spinning disc, and near black from subtractive mixing in the case of paints. At the end of the book, Harris describes the phenomenon of colored shadows. He explains that a stick placed in the orange light of a candle will cast a blue shadow, this result being predictable from the positions of orange and blue on opposite sides of his circle. A more extensive discussion of complementary colors can be found under that heading in this encyclopedia.
Johann Wolfgang von Goethe is best known as a writer of novels, plays, and poetry, but he also wrote a book on color theory which remains influential today. Goethe was satisfied that “yellow, blue, and red, may be assumed as pure elementary colours, already existing; from these, violet, orange, and green, are the simplest combined results” [12, p. 224]. When these six colors are arranged in a circle, yellow is opposite violet, blue is opposite orange, and red is opposite green. Goethe places great emphasis on such relationships: “the colours diametrically opposed to each other in this diagram are those which reciprocally evoke each other in the eye” [12, p. 21]. This can be recognized in afterimages and Goethe describes his experience of a “beautiful sea-green” when a girl wearing a scarlet bodice moved out of sight [12, p. 22]. He argues that such experiences show how the eye demands completeness. The red bodice gave way to green as a union of blue and yellow. Goethe saw in afterimages “a natural phenomenon immediately applicable to aesthetic purposes” [12, p. 320]. The afterimage phenomenon provides another way of defining complementary relationships with the added claim by Goethe that such relationships are beautiful. So Goethe is reinforcing the notion that the color circle can be seen as a tool for developing harmonious color combinations.
Michel-Eugène Chevreul developed a set of nine color circles, graded from full hue (Fig. 6) to almost black, and each with 72 hues, as the basis of a comprehensive color order system. In his introduction to a translation of Chevreul’s book De la loi du contraste simultané des couleurs, Faber Birren explains how “Chevreul devoted himself not only to color organization, color harmony, and contrast effects, but to methods of naming and designation of colors” [13, p. 29]. A special memorial edition of Chevreul’s book was published by the National Press of France in 1889 when Chevreul himself was 103 years old. The potential confusion between the physical and visual aspects of color is evident in a prefatory note to this edition: “In order to guarantee to the plates of this book the stability which their scientific nature requires … it was necessary to resort only to mineral colors whose stability was certain. … Since the three colors chosen by Chevreul as basic, red, yellow, blue, cannot be reproduced precisely by means of isolated materials, they were obtained by mixing” [13, p. 27]. If the “basic” colors red, yellow, and blue could only be obtained by mixing their status as “basic” would need to be clarified.
The Natural Color System (NCS)
The CIE Chromaticity Diagram
The Color Circle Today
Itten’s circle is attractive, clear, and memorable, but it needs to be viewed with caution. Itten was an artist writing for students of art. Artists work with pigments and so the “color classification must be constructed in terms of the mixing of pigments” [25, p. 21]. But Itten defines his primaries in terms of appearance: “a red that is neither bluish nor yellowish; a yellow that is neither greenish nor reddish; and a blue that is neither greenish nor reddish” [25, p. 29]. Itten refers to green in these definitions, as does Hering in his definitions of urfarben, and green is one of the elementary colors of the NCS. Nevertheless, for Itten, green is a secondary color, a mixture of blue and yellow.
From the experience of working with a number of different paints, it is possible to judge, from their appearance, how useful a group of paints will be in the mixing process. Students can be misled by the Itten diagram and may blame themselves if they are unable to mix a satisfactory range of colors from red, yellow, and blue primaries as these are defined by Itten. As Harald Arnkil points out, “anyone who has tried to create Itten’s twelve-hue color circle according to his requirements will be frustrated to a lesser or greater degree” [26, p. 88]. A more satisfactory range of colors can be mixed with paints that are closer in appearance to the cyan, magenta, and yellow inks as used by printers. This is demonstrated in the entry on “Primary Colors” in this encyclopedia.
Perhaps Itten could have acknowledged the shortcomings of available pigments and followed the example of Moses Harris by explaining how he “treats on colour in the abstract.” If the diagram is misleading as a guide to mixing paints, it is reasonable to wonder what purpose it is intended to serve. Arnkil asks this question and suggests that it may have been “associated with his idea of the 12-colour circle as the basis of colour harmony” [26, p. 88].
Itten follows Goethe in asserting the significance of the afterimage phenomenon for color harmony, and he claims that opposite colors in his circle are complementary. Harmonious color combinations can supposedly be found by drawing a regular geometric figure inside the circle. Lines passing through the center of the circle, equilateral triangles, isosceles triangles, squares, and rectangles, as they touch the colors in the circle, all point to harmonious color combinations. As well as complementary pairs, Itten illustrates harmonious triads and tetrads – combinations of three and four colors. No doubt this is a useful starting point for people who lack confidence, but closer scrutiny reveals a problem. Itten defines complementary relationships in three ways, all of which have been encountered in the work of others: subtractive mixing to near black (Harris), afterimages (Goethe), and additive mixing to neutral gray (Ostwald). The theory would be more convincing if these different ways of defining complementary relationships yielded the same pairs, but this is not always the case. The most dramatic variation is with blue. The complementary of blue is red-orange from subtractive mixture, yellow-orange as an afterimage, and yellow from additive mixture. If these pairs are to be opposite to each other in different circles, the distribution of hues would need to be adjusted.
An Elastic Color Circle
The color circle has a long history and is well established in color theory. It is used to represent colors as something physical, as lights, pigments, inks, or dyes, as well as colors as visual phenomena. It is used to illustrate relationships between colors, in systems of color classification and identification, as a guide to color mixing and as a tool in the search for harmonious color combinations. Although the sequence of hues is always the same, the intervals between hues can vary as the principles behind the construction of the circles varies. There is no single color circle that is “correct.” Rather than try to establish a single color circle as some kind of standard, or to insist on a single purpose for the color circle, it is more helpful to recognize that a color circle can embody a variety of information and that it may be necessary to stretch or compress the hues in the circle according to the information that is required.
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