An extract on #purple
Purple was the color worn by Roman magistrates; it became the imperial color worn by the rulers of the Byzantine Empire and the Holy Roman Empire, and later by Roman Catholic bishops. Similarly in Japan, the color is traditionally associated with the Emperor and aristocracy. The complementary color of purple is yellow.
The word 'purple' comes from the Old English word purpul which derives from Latin purpura, in turn from the Greek (porphura), name of the Tyrian purple dye manufactured in classical antiquity from a mucus secreted by the spiny dye-murex snail.
The first recorded use of the word 'purple' in the English language was in the year 975 AD. In heraldry, the word purpure is used for purple.
In the traditional color wheel used by painters, violet and purple are both placed between red and blue. Purple occupies the space closer to red, between crimson and violet. Violet is closer to blue, and is usually less saturated than purple.
While the two colors look similar, from the point of view of optics there are important differences. Violet is a spectral color it occupies its own place at the end of the spectrum of light first identified by Newton in 1672, and it has its own wavelength (approximately 380420 nm) whereas purple is a combination of two spectral colors, red and blue. There is no such thing as the "wavelength of purple light"; it only exists as a combination. See Line of purples.
Monochromatic violet light cannot be produced by the red-green-blue (RGB) color system, the method used to create colors on a television screen or computer display. (In fact, the only monochromatic colors of light that can be produced by this color system are the red, green, and blue that define it.) However, the system is capable of approximating it due to the fact that the L-cone (red cone) in the eye is uniquely sensitive to two different discontinuous regions in the visible spectrum its primary region being the long wavelength light of the yellow-red region of the spectrum, and a secondary smaller region overlapping with the S-cone (blue cone) in the shortest wavelength, violet part. This means that when violet light strikes the eye, the S-cone should be stimulated strongly, and the L-cone stimulated weakly along with it. By lighting the red primary of the display weakly along with the blue primary, a relatively similar pattern of sensitization can be achieved, creating an illusion, the sensation of extremely short wavelength light using what is in fact mixed light of two longer wavelengths. The resulting color has the same hue as pure violet; however, it has a lower saturation.
One curious psychophysical difference between purple and violet is their appearance with an increase in luminance (apparent brightness). Violet, as it brightens, looks more and more blue. The same effect does not happen with purple. This is the result of what is known as the BezoldBrcke shift.
While the scientific definitions of violet and purple are clear, the cultural definitions are more varied. The color known in antiquity as Tyrian purple ranged from crimson to a deep bluish-purple, depending upon how it was made. In France, purple is defined as "a dark red, inclined toward violet." The color called purple by the French, pourpre, contains more red and half the amount of blue of the color called purple in the United States and the U.K. In German, this color is sometimes called Purpurrot ("purple-red") to avoid confusion.