In color theory, a "purple" is defined as any non-spectral color between violet and red (excluding violet and red themselves). The spectral colors violet and indigo are not purples according to color theory but they are purples according to common English usage since they are between red and blue.

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 also associated with royalty and nobility (stemming from antiquity where Tyrian Purple was only affordable to the elites).

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 380-420 nm), 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 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; this line is known as the line of purples, or the purple line.

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.

Violet cannot be reproduced by a Red-Green-Blue (RGB) color system, and must be simulated by a mixture of red and blue (purple). The shade of violet simulated in the color box above is just over halfway between magenta and blue on the color wheel.

Properties

Tyrian purple: Classical antiquity

main: Tyrian purple