Nonspectral colors

It should be noted that purples are not included in the hst of spectral colors. The purples belong to a special class of colors they can be produced by mixing the light from two spectral lines, one in the red end of the spectrum, the other in the blue end. Purple (magenta is a more scientific name) is therefore referred to as a nonspectral color,... 

Figure 11.6 Chromatkity diagram or chart. Color as encoded in a VIS spectrum is described by plotting the chromaticity coordinates X and y points on the chart. The outer band contains spectral colors (ROYGBIV), and the connecting line consists of nonspectral colors, such as pink and purple. A colored version is found in the color insert. 

Achromatic colors are white, black, and gray. Black and gray differ from white only in their relative reflection of incident light. The purples are nonspectral chromatic colors. All other colors are chromatic for example, brown is a yellow of low lightness and low saturation. It has a dominant wavelength in the yellow or orange range. 

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