Colour theory

In the arts of painting, web design, and photography, color theory is a set of basic rules for mixing color to achieve a desired result. As pigment and light are different in terms of how they combine to create colors, so too are the rules for dealing with each. White light is composed of the mixture of the three primary hues red, green and blue. Black is approximated in pigment by mixing the primaries cyan, magenta and yellow (the imperfect primaries blue, red and yellow are the more traditional primaries due to their colorfast properties and physical pigment availability.)

Color models


On his Theory of Colors, Goethe proposed a symmetric color circle, which comprises both the Newtonian and complementary spectra. In contrast, Newton's color circle, with seven colors subtending unequal angles, did not exhibit the symmetry and complementarity that Goethe regarded as essential characteristics of color. For Newton, only spectral colors could count as fundamental. Goethe's more empirical approach led him to recognize the essential role of (nonspectral) magenta in a complete color circle.

Mixing colors of light, usually Red/Green/Blue, is done using the additive color system (also referred to as the "RGB Model" or "RGB color space"). The basis for these colors are the color-sensitive cone cells in the human retina. All the possible colors that can be created by mixing these three colored lights are referred to as the gamut of those particular lights. All these colors when mixed together in equal portions create white; when no color of light is present, one perceives black. Additive color applies to computer monitors, television, and video projectors, all of which use combinations of red, green, and blue phosphors.

For printing purposes and in painting, the colors used are cyan, magenta, and yellow; this model is called the "CMY model". In the CMY model, black is created by mixing all colors, and white is the absence of any colors (assuming a white medium). As colors are subtracted to produce white, this is also called the subtractive color model. A mix of Cyan, Magenta, and Yellow actually gives a muddy black so normally true black ink is used as well; when black is added, this color model is called the "CMYK model", where the K stands for "key". The CMY color model is also more accurate for pigment-mixing.

Also commonly used in painting is the RYB color model, in which red, yellow, and blue are the primary colors. It is possible to mix red, yellow (not green) and blue paint to get orange, purple and a non-primary shade of green paint, due to subtractive mixing. This model is largely used for traditional reasons; red and blue are in fact approximations for magenta and cyan respectively - the CMY color model can more easily display a full gamut of colors than can RYB.

A much more detailed discussion of color models, particularly as they apply to color for computer displays, can be found in the color space article.

Only fictional "primary" colors can mix all possible colors. These primaries are arbitrary concepts, used in mathematical models of color vision. They do not represent real color sensations, or even real nerve impulses or brain processes. In other words, all perfect "primary" colors are completely imaginary. For more details, see the color vision article.

On the other hand, any three (or four or five or six) real "primary" colors cannot mix all the colors in any medium, and this is always true no matter which "primary" colors are chosen and no matter which medium &#8212; inks, paints, dyes, filters, phosphors, artificial lights, or monospectral lights &#8212; is used to mix the colors. In other words, all mixable "primary" colors are incomplete or imperfect.

The color wheel
Traditionally colors are represented on a wheel of 12 colors: three primary colors, three secondary colors (created by mixing primary colors), and six tertiary colors (created by mixing the primary and secondary colors). Artists use a traditional color wheel based on the RYB model (red/yellow/blue) with secondary colors of orange, green, and purple. For all computer-based color, a wheel based on the RGB model is used; this encompasses the CMY model as well since cyan, magenta, and yellow are the secondary colors for red, green, and blue. (Conversely the secondary colors for cyan, magenta, and yellow are red, green, and blue.) In the RGB/CMY color wheel, orange is a tertiary color between red and yellow and purple is a tertiary color between magenta and blue.

Newton was the first to devise a color wheel (Newton's circle of colors); his differed from the modern one in going directly from violet to red: modern ones have purple between them. Newton only included spectral colors in his circle of colors; as a result, purple was ommitted.

Tints and shades
The color wheel is based on "pure" colors; for every color there are also darker and lighter versions. Darker versions are produced by adding black or removing light, and are called shades; they are sometimes also called "deep" or "dark" colors. Dark shades of yellow, oranges, and some reds are called browns by the Real Color Wheel. Lighter versions are produced by adding white or more light, and are called tints; they are also sometimes called "pale" or "light" colors. Very light tints are also often referred to as "pastel" colors; light tints of some reds, oranges, and yellow are tans.



Color harmony and color schemes
Harmonious colors are colors that work well together, that produce a color scheme that looks attractive; the color wheel can be used as a valuable tool for determining harmonious colors. Complementary colors are colors directly across from each other on the wheel. These are typically colors that will produce a strong contrast. Split complementary colors are those on either side of a complementary color; these colors contrast, but not as strongly as complementary colors. Triadic colors represent three colors equidistant on the color wheel; this typically provides a balanced color scheme with reasonable contrast. Analogous colors are colors next to each other on the color wheel. They typically harmonize well but may not provide enough contrast, and are perhaps best used in conjunction with a complementary color. Monochromatic colors are all shades and tints of the same color.

Cool and warm colors
Warm are all those that have a yellow undertone, such as bright red, oranges, yellows, and green-yellows, and are typically thought to express warmth, comfort, and energy. These colors also tend to make things stand out and advance towards you from the page or screen. Cool colors have a blue undertone, and include violets, blues, aquas, and greens. When they are used together, cool colors seem to move away from the viewer, and express coolness, detachment, stability, and calmness.

Neutral colors
Black, gray, and whites are neutral; browns, beiges, and tans are sometimes considered to be neutral as well. Neutral colors are intended to send no messages but often work harmoniously with other colors. They are sometimes thought of as colors "off the color wheel". Sometimes they are not neutral at all, see Goya's black paintings.

Neutrals may be created by mixing grey with pure colors or by mixing two complementary colors (opposite colors). The color made by mixing complements may be further neutralized by mixing grey.

Schemes from nature
Combinations of colors found in nature often work well as color schemes even if they don't fit specific patterns discussed above; examples of these schemes include "autumn colors" and "spring colors"

Color in painting
In painting the different color wheels or color solids are used as tools to teach beginners the essential relationships between color hues. The organization of colors on the various color wheels is very subjective, and may depend on whether a particular wheel is used for color perception, color psychology, or color mixing.

Traditional color theory using the RYB color wheel states that the primary colors (red, blue, yellow) combine to form the three secondary colors (purple, green, orange). A primary color will have a secondary color as its opposite &mdash; ergo red's complement is green, blue's is orange, and yellow's is purple. Adding a complementary color to a color on the canvas is the traditional technique for making shadows, as well as for choosing a balance of color overall, so that the eye does not tire from an overuse of red, for example.

Unfortunately, when used in practice, combining primary colors using the RYB color wheel often results in secondary colors that lack vibrancy or are "muddy" &mdash; appear as if they are "dirty" and turning brown. Mixing complementary colors does result in a darker color, but the resulting color may appear dull and muddy as well.

Mixing pigments using the CMY color wheel greatly reduces this problem. Combining CMY primary colors (cyan, magenta, and yellow) forms the three CMY secondary colors (blue, red, and green) in a more vibrant, purer form than the RYB color wheel. Complements around the wheel &mdash; cyan opposite red, magenta opposite green, and yellow opposite blue &mdash; are more properly matched, and when combined result in neutral dark grays and blacks instead of dark browns or muddy blacks.

Although in theory, one should be able to mix all colors using the CMY color wheel using just the pure pigments of cyan, magenta, and yellow, the mixed colors usually are still duller than their pure primary counterparts. This is especially apparent between cyan/magenta, and yellow/cyan. In order to obtain a more vibrant version of a mixed secondary color, one would replace the dull mixed hue with a more vibrant natural pigment secondary color of the same hue. For instance, mixing primaries hanza yellow and phthalocyanine cyan &mdash; effectively yellow and cyan &mdash; will result in a dull blue-green secondary color. In order to achieve a more vibrant blue-green, the natural pigment phthalocyanine green would be used. By replacing mixed secondary colors with natural pigment secondary colors, mixed tertiary colors will be more vibrant than mixed from the primaries alone.

Shadows
In most color theories, "shadows" generally refers to a general choice between adding black pigment, or using a complementary color to contrast a color, thereby making it darker by mixture or by optical illusion. The reason is that adding black to make a shadow tends to flatten the painting&mdash;neutralizing any dynamic color interactions that would otherwise occur. Adding a complement accomplishes the task of defining the darker area and, at the same time, adds another color, creating a more realistic and dimensional look.

Pigment
Depending on the quality of the paint, the balance between colors varies greatly with pigment. One way to test the quality of oil paints is to make a sample of black by mixing the primary hues. To produce black, blue and red are mixed to a dark purple, which is gradually bent toward a colorless black by adding smaller amounts of yellow. Testing the balance of the mixture simply requires separating a small portion and adding white spreading the grey out on the palette. If the grey is colorless, then the black is pure. Poor pigment quality makes a muddy, purplish/greenish glob, while better paints will blend to black or very close to it.

Color space

 * Munsell Colour System among the first quantification efforts of color space, still in use today
 * CIE 1931 color space also known as the CIE XYZ color space
 * CIE L*a*b* color space widely used in the paint industry
 * RGB color space commonly used for color monitors (based on the RGB color model)
 * CMYK color model for color printing and pigments
 * HSV color space (hue, saturation, value)
 * HLS color space (hue, lightness, saturation)
 * RYB color model the traditional color model used by artists.
 * YUV for PAL and NTSC television
 * YIQ - formerly used in NTSC television

Theories of color perception

 * Trichromatic theory
 * Opponent process

Subtle Color Psychology

 * Purkinje effect
 * Bezold-Brücke shift