It is important to understand the key terminologies and theories associated with describing and understanding colours.

Colour Description:

To give a precise description of a colour can be difficult and frustrating. A yellow can be dark-yellow or light-yellow, bright or dull yellow, lemon-yellow or melon-yellow. Colour has four distinct properties: hue, value, saturation. To understand colour you must understand how these four properties relate to each other.

Hue:
A hue name is the name of the colour which is used to describe a particular wavelength. The average person can distinguish about 150 colours (hues) of light and every one can be described using one or two of only six words- Red, orange, yellow, green, blue, violet. A colour is usually called by the name of its most obvious, or dominant, hue. A hue without any white, black, grey or complementary in it is called a pure hue.  Different hues can be obtained by mixing two primaries, two adjacent colours or two complementary colours in equal or unequal proportions.

Value:
Value is concerned with the light and dark properties of colour. All colours exhibit these properties. The hues have a natural value where they look the purest. Some colours, like yellow, are naturally light. Some, like violet, are darker. All hues can be made in all values. Adding white paint will make any pigment lighter. Adding black paint will make most pigments darker, but will cause yellow paint to shift in hue to green. Value can exist without hue (see achromatic). Black, white and gray are values without colour. White is the highest possible value while black is the lowest. Gray as the midpoint between black and white, is a medium value, neither dark nor light.

Saturation:
The third descriptive quality of colour is saturation, or chroma or intensity. It defines the degree of purity of a hue or the contrast between dull and vivid. Saturation is a comparative property and like value is linear and progressive. The beginning of a saturation scale is a colour that is hue- intense. The end step is a colour so muted that its hue can just be identified.

Temperature:
The temperature of a colour is its relative warmth or coolness. Cool and warm are two opposing qualities of hue. Cool colours contain blue or green: blues, greens, violets, and steps between them. Warm colours are reds, oranges, yellow, and steps between them. Colour temperatures affect us both psychologically and perceptually. They help determine how objects appear positioned in space. Warm colours are said to advance (they appear closer to the observer). Cool colours tend to recede (they appear farther from the observer).

Tints, Shades and Tones:

• Tints and Shades:
Pure hues are often diluted to change their value to make them lighter or darker. A tint is a hue that has been made lighter (by adding white). A shade is a hue that has been made darker (by adding black). Tinting a colour retain the hue while making it more light-reflecting. In contrast, shades reduce hue experiences. Black absorbs all wavelengths of light and hence, reduces light reflectance, dull and muted.

• Tones:
There is no really satisfactory definition for “tone.” It is defined as “pure colour diluted by black or white,” which we know as a tint or shade. A second definition states that tone is “one hue modified by another”(as in “this is a blue tone that is a greener one”). The third meaning is given as “a hue muted by gray.” Each definition means a modification of hue, but each means a different kind of modification of hue. The first means dilution by changing value, the second means dilution by changing hue, the third dilution by adding gray.

Colour Mixing:
Subtractive Mixing is the process of mixing pigments together as seen in paintings. This became an established fact in the printing and photographic industry, as well as in the craft of mixing paints and pigments in the beginning of the 20th century. Subtractive colour systems star t with light- white light. Collared dyes and filters between the viewer and the light source or reflective surface subtract wavelengths from the light, giving it colour. Yellow, Magenta and Cyan when mixed in various proportions, offer the largest possible subtractive colour range. Hence they are subtractive primaries. The secondary colours red, green and blue result from mixing two subtractive primaries in proper proportions, while black or at least a dark grey result from mixing proper proportions of all three of them.

The CMYK colour model is a subtractive colour model, used in colour printing, and is also used to describe the printing process itself. CMYK refers to the four inks used in some colour printing: cyan, magenta, yellow, and key (black). When two RGB colours are mixed equally they produce the colours of the CMYK model. Green and blue creates cyan (C), red and blue creates magenta (M), and red and green creates yellow (Y). Black is added to the model because it cannot be created with the 3 subtractive primaries. The K, or “key,” stands for black.

Additive colour mixing is the process of mixing coloured light, such as in theatres and televisions. Red, Green, Blue when mixed in various intensities, offer the largest possible additive colour range. Hence, these are the additive primaries. The secondary colours yellow, magenta and cyan blue result from mixing two additive primaries in proper intensities, while white results from mixing proper intensities of all three.

The RGB colour model is an additive colour model in which red, green, and blue light is added together in various ways to reproduce a broad array of colours. The main purpose of the RGB colour model is for the sensing, representation, and display of images in electronic systems, such as televisions and computers, though it has also been used in conventional photography. Additive colour mixtures were discovered in 1860 by Maxwell. Before the electronic age, the RGB colour model already had a solid theory behind it, based in human perception of colours.

Colour wheels, charts, tables, bars, etc allow us to organize different colours and predict the interactions between them. Among these, colour wheel remains the most common and convenient method for visually understanding and comparing the relationships of different hues. Colour circles have been used to describe associations of colours from ancient times, but the first known example of the representation of hue in the form of a wheel was designed by Sir Isaac Newton in 1666.

History of Colour Wheel:
Newton took the bar of colours created by the passage of light through a prism and transformed it into a segmented circle, where the size of each segment differed according to his calculations of its wavelength and of its corresponding width in the spectrum. The placement and size of the coloured sections of Newton’s circle suggested other mathematical and harmonic relationships.

Goethe’s ‘Theory of Colours’ in the early 19th century provided the first systematic study that focused on the physiological effects of colour rather than the effect of light. His two-dimensional wheel was based on triad of primaries – red, yellow and blue – with secondaries as the compliments of the primaries. Gothe formulated a colour triangle.

Runge published the book ‘the Colour sphere’ in 1810, in which he arranged 12 hues in a spherical format, giving us the first three dimentional colour model. His primaries were red, yellow and blue.

Munsell developed a colour system in 1905 ‘Colour Notation’, adopted by the United States Beareu of Standards as the acceptable language of colour. He stated that colour could be described according to three variables – hue, value and chroma. Munsell’s three-dimensional colour tree, hues are positioned on a vertical axis from light (top) to dark (bottom). Saturation was measured on a horizontal axis with dull-grey hues at the centre turning brighter towards the outer edges [1].

Newtons Colour Circle.

Mayer’s  Colour  Triangle:  Lichtenberg’s  replication  of Tobias Mayer’s triangle has only seven chambers per side, rather than Mayer’s.

http://www.colourlovers.com

Ignaz Schiffermüller, 1772 & Goethe, 1810.

Types of Colour Wheel:
The colour wheel is a visual representation of colour theory.  The different types of colour wheels are:

• The Pigment Wheel
• The Process Wheel
• The Munsell Wheel

• The Pigment Wheel:
The pigment wheel works with subtractive colours and gives information about the colour reactions when they are actually mixed.

. Primary colours:
A primary colour is the simplest hues and as the name suggests cannot be obtained by mixing. The primary colours are:
- Red
- Yellow
- Blue

. Secondary colours:
A secondary colour is an even interval between two primary parents. Each is the visual midpoint between two primary colours. The secondary colours are:

. Tertiary colours:
A Tertiary colour is created by mixing a primary colour and an adjacent secondary. It has no single hue apparent or dominating. A a colour that has been dulled slightly by addition of its complement is a muted hue not a tertiary colour.

When the three primary pigments of this wheel are combined muddy black is obtained. Moreover, secondary and tertiary hues are not equal mixtures of their components. Mixing equal amounts of yellow and blue pigments will produce green that is more yellow-green as yellow is stronger than green.

• The Process Wheel:
The Process Wheel has yellow, magenta and cyan as the tree basic primaries that result in purer hues when mixed as contrast to Pigment Wheel. This system is used in printing and photography.

When equal parts of primaries of this wheel are mixed the following secondary hues occur:

Again mixing the three primaries together in equal amounts produces black.

• The Munsell Wheel:
Munsell developed a partitive colour system based on five primary hues – yellow, red, green, blue and purple. His colour system was based on afterimage perceptions that are derived from hues that we see in nature. He set each after image as the compliment to the primary hues. He further systematised the colour wheel into a three-dimensional colour tree described earlier in this section.

[1] http://www.gutenberg-e.org
The chapter is based on the review of the following books:
Feisner E.A.,(2006) Colour StudiesSecond ed. Fairchild Piblications, NY.
Holtzschue, L. (2002) Understanding Color: An Introduction for Designers, John Wiley & Sons.
Pile, J. (1997) Color in Interior Design. McGraw-Hill companies Inc.