a color that has hue
a color that is part of the optical spectrum
The color of a monochromatic or nearly monochromatic light, i.e. a color to be found in the spectrum. Other colors are extraspectral.
Light of a single wavelength. When white light is separated by means of a prism, a continuum of the spectral colors red, orange, yellow, green, blue and violet is produced. A spectral color cannot be further separated.
A spectral color is a color that is evoked by the optical spectrum; every wavelength of light yields a different spectral color, in a continuous spectrum.