Purple is a general term for the range of shades of color occurring between red and blue. It is formed (in both subtractive pigment and additive light combinations) by mixing the primary colors red and blue in varying proportions, with possibly a very small quantity of the third primary color (green for light or yellow for pigment). There is disagreement over exactly which shades can be described as purple, some people preferring more precise terms such as magenta or heliotrope for particular shades. A difference in retinal sensitivity to red and blue light between individuals can cause further disagreement.

In color theory, a 'purple' is defined as any non-spectral color between violet and red. The spectral color violet is not a purple.

In art, purple is the color on the color wheel between magenta and violet and its tints and shades. This color, electric purple, is shown below.

In human color psychology, purple is associated with royalty, regality, and nobility (stemming from its use in heraldry to denote gentry).

Etymology and definitions

The word 'purple' comes from the Old English word purpul which originates from the Latin purpura. This in turn is derived from the Koine Greek (porphyra), name of the dye manufactured in Classical antiquity from the mucus-secretion of the hypobranchial gland of a marine snail known as the Murex brandaris or the spiny dye-murex.

The first recorded use of the word 'purple' in English was in the year AD 975.

Purple versus violet

main: Violet (color)

Violet is a spectral color (approximately 420–380nm), of a shorter wavelength than blue, while purple is a combination of red and blue or violet light. The purples are colors that are not spectral colors – purples are extra-spectral colors. In fact, purple was not present on Newton's color wheel (which went directly from violet to red), though it is present on modern ones, between red and violet. There is no such thing as the "wavelength of purple light"; it only exists as a combination.

On the CIE xy chromaticity diagram, violet is on the curved edge in the lower left, while purples are the straight line connecting the extreme colors red and violet.

One interesting psychophysical feature of the two colors that can be used to separate them is their appearance with increase of light intensity. Violet, as light intensity increases, appears to take on a far more blue hue as a result of what is known as the Bezold-Brücke shift. The same increase in blueness is not noted in purples.