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Hue is the term used to indicate the name of the colour, such as red, blue, or green. White light is broken down against a white background a spectrum appears, in which all the rainbow hues are spread out in a band. These colours, just as they appear in the spectrum, are commonly called normal colours.
The neutrals: Black, white and gray
Black results from the absence of colour or of light. A surface that absorbs all colour or all light rays will appear black. A surface that reflects all colours equally will appear white in white light. Gray is a neutral resulting from a mixture of pigments. It is an imperfect absorption of the light rays or a mixture of black and white.
Classes of colour
Colours may be divided into five classes (Fig.4.2): primary, binary, inter-mediate, tertiary, and quaternary.
- All colours may be obtained by mixing three fundamental hues: red (R), yellow (Y), and blue (B) in various proportions. These are called primary colours as they cannot be obtained by mixing other hues.
- When two primary colours are mixed in equal amounts a different hue will result. This new hue is called a binary or secondary colour. There are three binary colours – purple (P), called violet (V) in the Prang system, made by mixing red and blue; green (G), made by mixing yellow and blue; and orange (O), from red and yellow.
The primary and binary colours together are commonly called the six standard colours.
- When a primary and a neighboring binary are mixed an intermediate hue results. In appearance, the intermediate is halfway between the two colours. There are six of these intermediate hues: yellow-green (YG), blue-green (BG), blue-purple (BP) or blue-violet (BV), red-purple (RP) or red violet (RV), red- orange (RO), and yellow- orange (YO). So far the twelve hues that constitute the typical colour chart have been shown in fig 4.2.
- When two binary colours are mixed, a tertiary will be the result. The tertiary colours are yellow, blue, and red much neutralized. Tertiary yellow resembles a smoky yellow, the blue is known as slate blue, and tertiary red is the colour of old red brick. The following analysis illustrates how tertiaries are obtained: Tertiary yellow is a mixture of green and orange. Green is B+Y and orange is Y+R, and when they are mixed the colour will be predominantly yellow with some purple from the red and blue. This purple will neutralize part of the yellow leaving the colour, a grayed yellow. Tertiary blue is a mixture of purple and green, for R+B+B+Y gives principally blue dulled by orange from the R+Y. Tertiary red is orange mixed with purple, for Y+R+R+B gives red dulled by green from the Y+B.
- A mixture of two tertiary colours gives a quaternary. The quaternary colours are green, purple, and orange, much neutralized. They are sometimes spoken of as olive, prune and buff. Quaternary green is a mixture of the tertiaries yellow and blue. Tertiary yellow (B+Y+Y+R) added to tertiary blue (R+B+B+Y) gives this sum of colours – three parts of yellow, three parts of blue, and two parts of red. The result of the mixture is green, from the predominance of yellow and blue, and it is much dulled with the red. The quaternary purple is a mixture of the tertiaries blue and red. R+B+B+Y and Y+R+R+B make three parts of red and three parts of blue, giving purple, with two parts of yellow to dull it. Quaternary orange is tertiary red (Y+R+R+B) mixed with tertiary yellow (B+Y+Y+R). This makes three parts of yellow and three parts of red, which give orange, and the two parts of blue neutralize the orange.
Warm and cool hues
The hues will fall into two large groups in a colour wheel, divided by a vertical line (Fig.4.3). The colours at the right of the line near the blues are the cool hues, and those on the left side of the vertical line, around red and orange, are the warm. Red and orange are the warmest of all the colours, and they seem to advance the most and be the most conspicuous. Blue and blue-purple are the coldest hues, and they seem to recede and become inconspicuous. Green is between heat and cold, but it gets warmer as it grows yellowish, and cooler as it grows bluish. There is a harmony among the warm colours because they are related to one another, and the same harmony or family quality exists among the cool colours. The warm advancing hues will make objects appear larger and nearer to the observer, while the cool hues, which seem to recede, will appear to reduce size.
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