In view of the range of options available, to simply refer to a colour as ‘green’ would be of little value, so before considering the use of colour in design, it is useful to understand how colours can be varied and how they can be described for communication purposes. There are three measurable ingredients in any particular colour.

1. Hue. A hue is pure chromatic colour, containing no traces of any other colour, any black, white or grey. For example, red is a pure hue.
2. Chroma. Chroma relates to the saturation or intensity of mixtures of pure hues. For example, yellow with 30% red will make a specific chromatic version of orange. Yellow with 70% red will make a different specific chromatic version of orange.
3. Value. Value describes the effect of adding white, black or grey to any pure hue or chromatic variation. For example, blue with 50% white will be pale whereas blue with 50% black will be dark. Colours mixed with white are referred to as tints, mixed with black as shades and mixed with both, or grey as tones. The range of greys from white to black are referred to as neutrals.

Therefore, numerical reference to the percentages of ingredients in any particular mix will define its specific colour. There have been many attempts to classify colours for specification referencing in the construction industry, often reduced to a limited number of manageable standards. The full range of options is rarely necessary and a common understanding is often given based on British Standard reference numbers for a basic spread of choices. Although paint for example, can be obtained in many different colours, the choice of colour for a bathroom suite will generally be limited to the manufacturers standard range.

A more complex specification may be required for interior design work, for choosing decorative colours to match pre-coloured fixtures and fittings and for repair and maintenance work, when it may be important to try to match new colours with existing. Building materials are coloured in one of two ways, either as a result of an inherent natural finish belonging to the material, or by the application of an applied decorative finish. In both cases the colours mustbe selected to create the external appearance and the internal decor.