A hue is the color characteristic of a pigment, a particular chemical molecule, when illuminated by sunlight.
Of course such a molecule will not emit a single frequency of light, but will emit a spectrum of light at different frequencies and intensities. This depends on the absorption characteristics of the molecule and its emission characteristics. In some cases, for example, light energy can be absorbed at one frequency and re-emitted at different frequency. In any case, what results is a spectrum of color.
The eye perceives this spectrum as being of a single color, called the pigment's hue. https://physics.stackexchange.com/questions/ask My question is whether this hue is truly indistinguishable from energy emitted purely at that frequency. For example, the pigment vermillion, mercuric sulfide, has a nominal wavelength of 607nm. If we create a pure light source of that frequency only, is it indistinguishable from the light of the pigment to the eye?