Color mixing.

There are two ways to mix colour – ‘additive’ and ‘subtractive’.
Additive colour is the mixture of coloured lights. Three primary colours of red, green and blue when mixed together in equal colours produce white light. Mixing the three additive primaries in differing amounts of coloured light can create any colour in the rainbow. Colour televisions use the principle of additive colour mixing.

In subtractive colour mixing the principle is exactly the opposite. The subtractive primary colours are cyan, yellow and magenta. When mixed together they subtract from the light producing black. When different pairs of the subtractive primaries are mixed, the colour red, green and blue are produced. These principles are used when we paint and in photography and colour printing.
Colour systems. As the human eye can distinguish between 10 million colours, it is clear that to describe colour experiences by name is imprecise. While everyone knows what is meant by tomato red, different people have different ideas as to exactly what colours are meant by beige and sand; mauve and lilac. In order to accurately describe or pinpoint colours, a reference or colour system is required.
All the attempts to notate colour can be traced back to the work of Sir Isaac Newton. In 1660 he re-created a spectrum by directing a narrow beam of white light through a prism; he went on to develop a colour wheel by taking the two ends and bending the spectrum into a circle. This colour wheel evolved and changed over the centuries and in 1810 Otto Runge created a spherical model, with white at the North Pole and black at the South Pole and with Newton’s colour circle forming its equator. In 1915 William Ostwald devised his double-cone colour solid; also in 1915, Albert Munsell developed another system of colour notation that added steps to the constituent hues.
Munsell allowed his three-dimensional colour solid to respond in shape to the different potential strengths between hues, creating an asymmetrical colour solid. His colour model can be explained in three dimensions, in terms of hue, value and chroma. Hue is the ‘colour’ of a colour, i.e., its redness, greenness or yellowness, value refers to the amount of lightness or darkness, while chroma refers to its saturation or its colour strength.
A number of commercial colour specification ranges have been developed from Munsell’s work including the BS4800 and the Pantone and Colour Dimension systems. In textiles and clothing, the Pantone system is probably the most commonly used, and a whole range of products is available in its defined colours. These include ranges of marker pens, paper and even fabric samples.
Colour psychology. There is a commonly held belief that red is exciting and green calming. But which red and which green? Research has shown that strong greens, yellows and blues are all seen to be as exciting as strong red. The same research also showed that pale and dark versions of the same hues have quite the reverse effect. Pink has a calming effect on violent people. A common belief is that blue increases the size of a room while red has the opposite effect. Recent research, however, has shown that it is not the colour itself that has this effect but rather its value, the amount of whiteness or blackness. However, with regard to temperature, colour does have a very definite effect. Red and yellow rooms are perceived to be warmer than blue and green rooms.