Complementary colours

Chevreul's 1855 "chromatic diagram" based on the RYB colour model, showing complementary colours and other relationships

Main article: Complementary colour

For the mixing of coloured light, Isaac Newton's colour wheel is often used to describe complementary colours, which are colours which cancel each other's hue to produce an achromatic (white, grey or black) light mixture. Newton offered as a conjecture that colours exactly opposite one another on the hue circle cancel out each other's hue; this concept was demonstrated more thoroughly in the 19th century.

A key assumption in Newton's hue circle was that the "fiery" or maximum saturated hues are located on the outer circumference of the circle, while achromatic white is at the centre. Then the saturation of the mixture of two spectral hues was predicted by the straight line between them; the mixture of three colours was predicted by the "centre of gravity" or centroid of three triangle points, and so on.

Primary, secondary, and tertiary colours of the RYB colour model

According to traditional colour theory based on subtractive primary colours and the RYB colour model, which is derived from paint mixtures, yellow mixed with violet, orange mixed with blue, or red mixed with green produces an equivalent grey and are the painter's complementary colours. These contrasts form the basis of Chevreul's law of colour contrast: colours that appear together will be altered as if mixed with the complementary colour of the other colour. Thus, a piece of yellow fabric placed on a blue background will appear tinted orange, because orange is the complementary colour to blue.

However, when complementary colours are chosen based on definition by light mixture, they are not the same of the artists' primary colours. This discrepancy becomes important when colour theory is applied across media. Digital colour management uses a hue circle defined around the additive primary colours (the RGB colour model), as the colours in a computer monitor are additive mixtures of light, not subtractive mixtures of paints.

One reason the artist's primary colours work at all is that the imperfect pigments being used have sloped absorption curves, and thus change colour with concentration. A pigment that is pure red at high concentrations can behave more like magenta at low concentrations. This allows it to make purples that would otherwise be impossible. Likewise, a blue that is ultramarine at high concentrations appears cyan at low concentrations, allowing it to be used to mix green. Chromium red pigments can appear orange, and then yellow, as the concentration is reduced. It is even possible to mix very low concentrations of the blue mentioned and the chromium red to get a greenish colour. This works much better with oil colours than it does with watercolours and dyes.

So the old primaries depend on sloped absorption curves and pigment leakages to work, while newer scientifically derived ones depend solely on controlling the amount of absorption in certain parts of the spectrum.

Another reason the correct primary colours were not used by early artists is that they were not available as durable pigments. Modern methods in chemistry were needed to produce them.

Warm vs. cool colours

The distinction between 'warm' and 'cool' colours has been important since at least the late 18th century.[1] It is generally not remarked in modern colour science or colourimetry in reference to painting, but is still used in design practices today. The contrast, as traced by etymologies in the Oxford English Dictionary, seems related to the observed contrast in landscape light, between the "warm" colours associated with daylight or sunset and the "cool" colours associated with a grey or overcast day. Warm colours are often said to be hues from red through yellow, browns and tans included; cool colours are often said to be the hues from blue green through blue violet, most greys included. There is historical disagreement about the colours that anchor the polarity, but 19th-century sources put the peak contrast between red orange and greenish blue.

Colour theory has described perceptual and psychological effects to this contrast. Warm colours are said to advance or appear more active in a painting, while cool colours tend to recede; used in interior design or fashion, warm colours are said to arouse or stimulate the viewer, while cool colours calm and relax. Most of these effects, to the extent they are real, can be attributed to the higher saturation and lighter value of warm pigments in contrast to cool pigments. Thus, brown is a dark, unsaturated warm colour that few people think of as visually active or psychologically arousing.

Contrast the traditional warm–cool association of colour with the colour temperature of a theoretical radiating black body, where the association of colour with temperature is reversed. For instance, the hottest stars radiate blue light (i.e., with shorter wavelength and higher frequency) and the coolest radiate red.

The hottest radiating bodies (e.g. stars) have a "cool" colour while the less hot bodies radiate with a "warm" colour. (Image in mired scale.)

Achromatic colours

Any colour that lacks strong chromatic content is said to be unsaturated, achromatic, or near neutral. Pure achromatic colours include black, white and all greys; near neutrals include browns, tans, pastels and darker colours. Near neutrals can be of any hue or lightness.

Neutrals are obtained by mixing pure colours with white, black or grey, or by mixing two complementary colours. In colour theory, neutral colours are colours easily modified by adjacent more saturated colours and they appear to take on the hue complementary to the saturated colour. Next to a bright red couch, a grey wall will appear distinctly greenish.

Black and white have long been known to combine well with almost any other colours; black decreases the apparent saturation or brightness of colours paired with it, and white shows off all hues to equal effect.

Tints and shades

When mixing coloured light (additive colour models), the achromatic mixture of spectrally balanced red, green and blue (RGB) is always white, not grey or black. When we mix colourants, such as the pigments in paint mixtures, a colour is produced which is always darker and lower in chroma, or saturation, than the parent colours. This moves the mixed colour toward a neutral colour—a grey or near-black. Lights are made brighter or dimmer by adjusting their brightness, or energy level; in painting, lightness is adjusted through mixture with white, black or a colour's complement.

It is common among some painters to darken a paint colour by adding black paint—producing colours called shades—or lighten a colour by adding white—producing colours called tints. However it is not always the best way for representational painting, as an unfortunate result is for colours to also shift in hue. For instance, darkening a colour by adding black can cause colours such as yellows, reds and oranges, to shift toward the greenish or bluish part of the spectrum. Lightening a colour by adding white can cause a shift towards blue when mixed with reds and oranges. Another practice when darkening a colour is to use its opposite, or complementary, colour (e.g. purplish-red added to yellowish-green) in order to neutralize it without a shift in hue, and darken it if the additive colour is darker than the parent colour. When lightening a colour this hue shift can be corrected with the addition of a small amount of an adjacent colour to bring the hue of the mixture back in line with the parent colour (e.g. adding a small amount of orange to a mixture of red and white will correct the tendency of this mixture to shift slightly towards the blue end of the spectrum).

Split primary colours

In painting and other visual arts, two-dimensional colour wheels or three-dimensional colour solids are used as tools to teach beginners the essential relationships between colours. The organization of colours in a particular colour model depends on the purpose of that model: some models show relationships based on human colour perception, whereas others are based on the colour mixing properties of a particular medium such as a computer display or set of paints.

This system is still popular among contemporary painters, as it is basically a simplified version of Newton's geometrical rule that colours closer together on the hue circle will produce more vibrant mixtures. However, with the range of contemporary paints available, many artists simply add more paints to their palette as desired for a variety of practical reasons. For example, they may add a scarlet, purple and/or green paint to expand the mixable gamut; and they include one or more dark colours (especially "earth" colours such as yellow ochre or burnt sienna) simply because they are convenient to have premixed. Printers commonly augment a CYMK palette with spot (trademark specific) ink colours.

Colour harmony

It has been suggested that "Colours seen together to produce a pleasing affective response are said to be in harmony". However, colour harmony is a complex notion because human responses to colour are both affective and cognitive, involving emotional response and judgement. Hence, our responses to colour and the notion of colour harmony is open to the influence of a range of different factors. These factors include individual differences (such as age, gender, personal preference, affective state, etc.) as well as cultural, sub-cultural and socially-based differences which gives rise to conditioning and learned responses about colour. In addition, context always has an influence on responses about colour and the notion of colour harmony, and this concept is also influenced by temporal factors (such as changing trends) and perceptual factors (such as simultaneous contrast) which may impinge on human response to colour. The following conceptual model illustrates this 21st century approach to colour harmony:

Wherein colour harmony is a function (f) of the interaction between colour/s (Col 1, 2, 3, …, n) and the factors that influence positive aesthetic response to colour: individual differences (ID) such as age, gender, personality and affective state; cultural experiences (CE), the prevailing context (CX) which includes setting and ambient lighting; intervening perceptual effects (P) and the effects of time (T) in terms of prevailing social trends.

In addition, given that humans can perceive over 2.8 million different hues, it has been suggested that the number of possible colour combinations is virtually infinite thereby implying that predictive colour harmony formulae are fundamentally unsound. Despite this, many colour theorists have devised formulae, principles or guidelines for colour combination with the aim being to predict or specify positive aesthetic response or "colour harmony". Colour wheel models have often been used as a basis for colour combination principles or guidelines and for defining relationships between colours. Some theorists and artists believe juxtapositions of complementary colour will produce strong contrast, a sense of visual tension as well as "colour harmony"; while others believe juxtapositions of analogous colours will elicit positive aesthetic response. Colour combination guidelines suggest that colours next to each other on the colour wheel model (analogous colours) tend to produce a single-hued or monochromatic colour experience and some theorists also refer to these as "simple harmonies". In addition, split complementary colour schemes usually depict a modified complimentary pair, with instead of the "true" second colour being chosen, a range of analogous hues around it are chosen, i.e. the split compliments of red are blue-green and yellow-green. A triadic colour scheme adopts any three colours approximately equidistant around a colour wheel model. Feisner and Mahnke are among a number of authors who provide colour combination guidelines in greater detail.

Colour combination formulae and principles may provide some guidance but have limited practical application. This is because of the influence of contextual, perceptual and temporal factors which will influence how colour/s are perceived in any given situation, setting or context. Such formulae and principles may be useful in fashion, interior and graphic design, but much depends on the tastes, lifestyle and cultural norms of the viewer or consumer.

As early as the ancient Greek philosophers, many theorists have devised colour associations and linked particular connotative meanings to specific colours. However, connotative colour associations and colour symbolism tends to be culture-bound and may also vary across different contexts and circumstances. For example, red has many different connotative and symbolic meanings from exciting, arousing, sensual, romantic and feminine; to a symbol of good luck; and also acts as a signal of danger. Such colour associations tend to be learned and do not necessarily hold irrespective of individual and cultural differences or contextual, temporal or perceptual factors. It is important to note that while colour symbolism and colour associations exist, their existence does not provide evidential support for colour psychology or claims that colour has therapeutic properties.