colour

The mixing of the primary (red, blue, and green) coloured beams of light. All the colours mixed together produce white.

A prism (a triangular block of transparent material such as plastic, glass, or silica) is used to split a ray of white light into its spectral colours.

In physics, wavelength, or mixture of wavelengths, of light emitted or reflected from an object; in psychology, the subjective visual response to that combination of wavelengths. Visible white light consists of electromagnetic radiation of various wavelengths, and if a beam is refracted through a prism, it can be spread out into the visible spectrum (the part of the electromagnetic spectrum that can be detected by the human eye), in which the various colours correspond to different wavelengths. From long to short wavelengths (from about 700 to 400 nanometres) the colours are conventionally divided into red, orange, yellow, green, blue, indigo, and violet, though they merge smoothly into each other.

The colour of grass is green because grass absorbs some colours from the spectrum and those that it transmits or reflects are predominantly of wavelengths corresponding to green. A sheet of white paper reflects all the colours of the spectrum from its surface; black objects absorb all the colours of the spectrum.

Almost all colours can be visually matched by mixing proportions of red, green, and blue light. These are known as the additive primary colours. Different colour filters can also produce light of different colours. For example, a red filter transmits predominantly red light, the remaining colours of the spectrum being largely absorbed by the filter.

Mixing red, green, and blue light in the correct proportions produces white light. When these colours are mixed in different proportions, so-called secondary colours are formed; for example, blue + red = magenta, red + green = yellow, and green + blue = cyan. Yellow light is reflected from the surfaces of some flowers as the petals absorb blue light. Red and green light are reflected back, and these mix to give the sensation of yellow. However, yellow is also seen when monochromatic (single-wavelength) light of about 600 nanometres is reflected.

The light entering our eyes is either emitted by hot or luminous objects, or reflected from the objects we see.

Emitted light Sources of light have a characteristic spectrum or range of wavelengths. Hot solid objects emit light with a broad range of wavelengths, the maximum intensity being at a wavelength that depends on the temperature. The hotter the object, the shorter the wavelengths emitted, as described by Wien's displacement law. Low-pressure gases, such as the vapour of sodium street lights, can emit light at discrete wavelengths. The pattern of wavelengths emitted is unique to each gas and can be used to identify the gas (see spectroscopy).

Reflected light When an object is illuminated by white light, some of the wavelengths are absorbed and some are reflected to the eye of an observer. The object appears coloured because of the mixture of wavelengths in the reflected light. For instance, a red object absorbs most of the light falling on it except the light at the red end of the spectrum. This process of subtraction also explains why certain mixtures of paints produce different colours. Blue and yellow paints when mixed together produce green because between them the yellow and blue pigments absorb all wavelengths except those around green. A suitable combination of three pigments – cyan (blue-green), magenta (blue-red), and yellow – can produce almost any colour when mixed. This fact is used in colour printing, although additional black pigment is added. Cyan, magenta, and yellow are called the subtractive primary colours.

Primary colours In the light-sensitive lining of the human eyeball (the retina), cells called cones are responsible for colour vision. There are three kinds of cones. Each type is most sensitive to one colour only, either red, green, or blue. The brain combines the signals sent from the set of cones to produce a sensation of colour. When all cones are stimulated equally the sensation is of white light. The three colours to which the cones respond maximally are the additive primary colours mentioned above. By mixing lights of these three colours, it is possible to produce almost any colour. This process is called additive colour mixing, and is used to produce the colour on a television screen, the inside of which is coated with glowing phosphor dots of red, green, and blue.

Complementary colours Pairs of colours that produce white when mixed, such as yellow and blue, are called complementary colours.

Classifying colours Many schemes have been proposed for classifying colours. The most widely used is the Munsell scheme, which classifies colours according to their hue (dominant wavelength), saturation (the degree of whiteness), and lightness (intensity).

colour

In art, one of the most powerful of the visual or formal art elements, and a property of light. Specifically, colour is the quality or wavelength of light emitted or reflected from an object. Colours may be produced by the use of pigment (paint or dye), by the choice of naturally coloured objects, or (in installation art) by the use of lights or television screens.

Colour is best understood by breaking it into three areas of examination – hue, value, and saturation or intensity. Hue is what gives a colour its name. Within the study of hue there exist other terms such as: subtractive colour; additive colour; primary, secondary, and intermediate or tertiary colours; and complementary colours. Value, not only a property of colour, but also a formal art element in itself, concerns the lightness and darkness of a colour. Saturation or intensity describes the brightness or dullness of a colour. Colour interactions, namely hue, value, and intensity interactions, the study of certain combinations of colours (or colour schemes), and using colour as a means of expression, are all extremely important if the artist is to exploit the use of colour as one of the most powerful means of visual communication.

Hue Hue is the name of a colour. An infinite number of hues can be made through a process of mixing, accomplished either by using coloured lights, called additive colour, or by using pigment, known as subtractive colour.

Additive colour generally means the mixing of coloured lights. When all of the colours are combined, the result is white. Additive colour is not normally used by artists (artists mainly use pigment hues). However, in the 19th-century, artists began to use the ‘divisionist’, or pointillist, technique of painting separate spots of primary colour to blend in the spectator's eye. This new procedure involved the concept of additive colour, in the same way as separate beams of coloured light superimposed on a screen create a full colour image. The primaries of additive colour are red, blue, and green.

The colour used by artists when they mix pigments is what physicists call subtractive colour. Pigments behave in the same way the surface of an object does, their physical properties absorbing certain colours to leave the ones that are seen. In other words, an object appears a certain colour because its surface is absorbing the other colours of the spectrum, thus ‘subtracting’ them from the white light falling upon it. For example, the surface of a red book is absorbing wavelengths other than red, subtracting them from white so that only red is reflected. The primaries of subtractive colour are yellow, blue, and red. Opposite to additive colour, when the primary subtractive hues are combined the result, theoretically, is black. See also colour (physics).

Various mixes of the pigments (the primary subtractive colours), comprise the secondary colours, and the intermediate, or tertiary, colours. The primary pigment colours are yellow, red, and blue, and using these three colours in varying proportion it should be possible to mix any colour on the colour wheel (an arrangement of hues in a circular format). Mixing two primary colours creates the secondary colours: orange, green, and violet. Yellow and red make orange, blue and yellow make green, and blue and red make violet. On the colour wheel, secondary colours are placed between their primary colours. The tertiary or intermediate colours are created by mixing a primary and a secondary colour, or using an unequal mixing of only primary colours. For example, blue and violet makes the tertiary colour blue-violet, or the same colour can be made by mixing two-parts blue with one part red. Other tertiary colours include; yellow-orange, red-orange, red-violet, blue-green, and yellow-green. On the colour wheel, the tertiary colours are placed between the primary and secondary colours that form them.

Complementary colours are those hues that are directly across from each other on the colour wheel. For example, red and green or yellow and violet. Complementary colours are the exact opposite in hue; red, a primary colour, shares nothing with its complement green, made from yellow and blue. The significance of complementary colours can be seen in the study of colour interaction.

Value One of the formal art elements, but also part of the study of colour, value is the lightness or darkness of a colour, achieved by adding either white or black to the hue. Every colour has a ‘normal’ value; this is the value normally seen on the colour wheel. Adding white or black to the colour will alter its value by either tinting it up (adding white) or shading it (adding black). Hues also vary in tone, according to the overall amount of light they reflect. Using only shades and tints of one colour in a painting is known as monochromatic (or one-colour) painting, and can produce some of the most harmonious schemes.

Saturation Saturation, or intensity, refers to the brightness or dullness of a colour. Pure colours are of high-intensity, while dull hues are of low-intensity. Pigments on the colour wheel are as bright as they can be; it is only when a colour is mixed with its complement (its opposite) that the intensity will lessen. For example, red mixed with yellow will form an orange of equal intensity, but red mixed with green will form a colour of a lower intensity. The result of mixing equal parts of complementary colours is, theoretically, a neutral grey.

Colour interactions and schemes In order for artists and designers to achieve the finest results, it is necessary to know how colours interact and understand the effects produced by different colour schemes.

Colour interactions are the visual changes that occur in a colour's hue, value, and intensity, depending on the presence and juxtaposition of other colours in the composition. Hues are altered depending on the combination of colours used. For example, red-orange will look more red when it is next to orange, but will look more orange when it is placed beside red. Values can change depending on where colours are placed. For example, light shades look darker on a light background and appear light on dark backgrounds. The intensity of a colour is also dependent on other colours. A colour will seem more intense next to a neutral colour than it will next to another bright colour.

Complementary colours will also change depending on their surroundings. For example, subjective colours occur when the eye looks at a certain hue and imagines the complementary colour in the surrounding area, as with the purple shadow of a yellow object. The Impressionists used subjective colours to enforce contrast.

Colour schemes, or agreeable combinations of colours, can be achieved in a number of ways. Some of the main colour schemes used by artists are monochromatic, analogous, warm or cool colour schemes, triad, and split-complementary. Monochromatic schemes use only shades and tints of one colour. An analogous colour scheme consists of using hues next to each other on the colour wheel; for example, using only yellow, yellow-orange, orange, and red-orange in a composition. Warm colours (yellow, red, and orange) are called such because they evoke thoughts of warmth, heat, and excitement; calming cool colours (violet, green, and blue) recall cool objects such as the grass or sea. Artists use a warm or cool colour scheme to elicit a certain response from the viewer. Triad colour schemes employ three equidistant colours on the colour wheel, such as the primaries or all three secondary colours. Split-complementary colour schemes consist of a hue plus the two colours on either side of its complement, such as red with yellow-green and blue-green. In applying these schemes to pictorial design, painters distinguish between interpretive (expressive) and decorative colour. Sometimes painters will use a limited palette of fewer colours to make contrasts seem more subtle.

Expressive colour Colours themselves, when used in a certain way, are effective enough to expresses mood, feeling, and idea. Some artists rely on colour alone to elicit a response. For example, blue generally evokes a feeling of sadness, while red could represent excitement. Individuals respond differently to certain colours. Throughout art history artists have used colour as their primary source of communication. Expressionist painters, such as Edvard Munch, are noted for their dependence on colour in the creation of their work.

colour

In music, the quality or timbre of an instrument or voice. A ‘dark’ sound denotes a thick, heavy sonority while a ‘light’ sound describes a thinner, more transparent sonority. The Russian composer and pianist Aleksandr Skriabin invented a keyboard which would project colours on to a screen in order to reflect the mood and character of the music.

colour

In elementary particle physics, a property of quarks analogous to electric charge but having three states, denoted by red, green, and blue. The colour of a quark is changed when it emits or absorbs a gluon. The term has nothing to do with colour in its usual sense. See quantum chromodynamics.