As the name of a color, violet (named after the flower violet) is used in two senses: first, referring to the color of light at the short-wavelength end of the visible spectrum, approximately 380–420 nm when indigo is recognized, or more commonly 380–450 nm (this is a spectral color). Second, violet may refer to a shade of purple, that is, a mixture of red and blue light, and not a spectral color (see a discussion of the distinction between violet and purple). Spectral violet is outside the gamut of typical RGB color spaces, and although it can be approximated by that color shown below as electric violet, it cannot be reproduced exactly on a computer screen.
The color at right is called color wheel violet because, by its color formula, it is the color precisely halfway between magenta and blue on the HSV color wheel. It is also called near violet because this color, when plotted on the CIE chromaticity diagram is equivalent to a visual stimulus of approximately 422 nanometers on the spectrum, barely on the violet side of the transition between the violet and indigo parts of the spectrum, which occurs at approximately 420 nanometers if indigo is accepted as a spectrum color.
Compare the subtractive colors to the additive colors in the two primary color charts in the article on primary colors to see the distinction between electric colors as reproducible from light on a computer screen (additive colors) and the pigment colors reproducible with pigments (subtractive colors); the additive colors are a lot brighter because they are produced from light instead of pigment.
Pigment violet (web color dark violet) represents the way the color violet was always reproduced in pigments, paints, or colored pencils in the 1950s. By the 1970s, because of the advent of psychedelic art, artists became used to brighter pigments, and pigments called "Violet" that are the pigment equivalent of the electric violet reproduced in the section above became available in artists pigments and colored pencils. (When approximating electric violet in artists pigments, a bit of white pigment is added to pigment violet.)
The so-called web color "violet" is in actuality not really a tint of violet, a spectral color, but a non-spectral color. The web color violet is actually a rather pale tint of magenta because it has equal amounts of red and blue (the definition of magenta for computer display), and some of the green primary mixed in, unlike most other variants of violet that are closer to blue. This same color appears as "violet" in the X11 color names.