In color theory, the line of purples or the purple boundary is the locus of non-spectral colors on the edge of the chromaticity diagram between red and violet. Like spectral colors, purples can be considered fully saturated in the sense that for any given point on the line of purples there exists no color more saturated than it. But there is no monochromatic light source able to generate a purple color. Instead, every color on the line of purples is produced by mixing a unique ratio of extreme red and extreme violet (which, as being consistently more reddish than the bluish violet, may be considered purple anyway;[1] see Bezold–Brücke shift).
Unlike spectral colors (which may be implemented, for example, by nearly monochromatic light of laser, with precision much finer than human chromaticity resolution), colors on the line of purples are more difficult to implement practically. Cones' sensitivity to both of extreme spectral colors is quite low (see luminosity function), so commonly observed purple colors do not achieve maximal saturation.
Purple colors with high saturation include crimson, amaranth, raspberry, ruby, rose, and magenta, as well as purple itself. Some of the brighter tones of pink tending towards rose and magenta such as hot pink, deep pink, and shocking pink are also regarded as purple colors in color theory.