The perception of colour is a sensory experience. The colour of an object is seen by the eye when white light is shone upon the object's surface. The surface reflects some colours and absorbs others. It is the reflected light (or wavelength) that is picked up by the eye. For example, a cherry is reflecting red light and absorbing other colours.
Within the eye, the retina contains receptors called rods and cones. The cones react to colour wavelengths whilst the rods react to brightness. There are three types of cone: red, green and blue. Each colour has a different wavelength - blues, greens and violets have shorter wavelengths, while reds, oranges and yellows have longer wavelengths. When colour wavelengths fall on the retina, the brain interprets the signals as colour.
Colour attributes
There are three attributes of colour: hue, saturation and lightness. These terms are often used to describe aspects of colour. Having a basic understanding of these terms will help you to understand colour.
Hue
Hue is essentially the names given to a colour or colour family, for example red, green, blue and yellow. It typically refers to pure colour - without added white or black. The ability to discriminate between different hues can be diminished for many with colour vision defects.
Saturation
Saturation is the strength of a colour. Colours can be described as strong or pale. When displaced with white or grey a colour becomes desaturated.
Lightness
The lightness (or luminance) of a colour is a measure of how bright a colour is, which is considered as adding pure white to a colour. For more details go to colour contrast or tips for effective colour use.
How is colour defined in design?
There are different ways to define colour particularly within design. The most common terms used are the colour values RGB and CMYK, described below. Understanding how colour is produced will help a designer decide which colour value to use when creating images on the computer.
RGB
RGB stands for red, green and blue. These are known as additive primary colours. When red, green and blue light are added together in equal quantities they produce white, whilst the absence of these colours create black. In theory, all colours of the spectrum can be created by combining different amounts of red, green and blue light.
Computer monitors display colour using RGB. If creating work to be used on screen only, then RGB will be the most effective mode to use. Within the RGB system, each colour has a numeric value with 0 being dark and 255 being bright, therefore listing a numeric value for red, green and blue will create a particular colour.
CMYK
CMYK stands for cyan, magenta, yellow and black. These are known as subtractive primaries. Before the colours are mixed, they are considered pure; when mixed they are not pure as the colours have been combined, hence the term subtractive. Printers use CMYK, sometimes referred to as 'four-colour printing.' Numeric values are also assigned to CMYK based on percentage values; 0% is the lightest with 100% being the darkest, therefore defining percentage values to CMYK will create a specific colour.
Computer screens and printers display and produce colour in different ways, which results in the variation of colour in a printed image and what is seen on screen. Care must be taken when working with colour on screen as the colour chosen may not be the colour which is printed.