Hello gang. First post. Maybe this can help:
Beyond the locus of spectrally pure colors
Mark D. Fairchild* Munsell Color Science Laboratory, RIT, Rochester, NY, USA 14623-5604
The spectrum locus of a CIE chromaticity diagram defines the boundary within which all physically realizable color stimuli must fall. While that is a physical and mathematical reality that cannot be violated, it is possible to create colors that appear as if they were produced by physically impossible stimuli. This can be accomplished through careful control of the viewing conditions and states of adaptation.
The CIE 1931 xy chromaticity diagram is widely recognized by the horseshoe shape of the spectrum locus. This locus of spectrally pure colors is simply defined by the standard color matching functions, the computation of chromaticity coordinates, and the fundamental limitation of monochromatic stimuli that have energy at a single wavelength and no energy at any other visible wavelength.1 More commonly, the spectrum locus is referred to as defining the boundary of the gamut of all physically possible colors. This, however, is an error. The spectrum locus does define the gamut boundary for physically possible stimuli, but it does not limit the color appearance of stimuli. Specification of color appearance requires more information about the stimulus and adaptation state of the observer2 and it is entirely feasible that a stimulus in one viewing condition might appear to be produced by a stimulus from beyond the locus of spectrally pure colors in some other reference viewing condition.