Number of colors generated by smooth nonfluorescent reflectance spectra.

In this study, we have analyzed statistical properties of the values of the first- and second-order derivatives of spectral reflectance curves. We show that values of all four tested spectral data sets have very similar statistical properties. We set outer limits that bound the clear majority of the values of the first- and second-order derivatives. These limits define smoothness of all nonfluorescent reflectance curves, and they can be used to form a new object color solid inside classical MacAdam limits, including all possible colors generated by smooth nonfluorescent reflectance spectra. We have used the CIELAB color space and filled the new object color solid with a hexagonal closest packing-point lattice to estimate that there exist about 2.5 million different colors, when viewed under the D65 standard illumination.