hue purity of watercolor paints
This page publishes my calculations of the hue purity of generic watercolor paint pigments, as explained in the section on hue purity and optimal colors.
This page includes CIECAM coordinates, averaged across all paint brands, for over 170 pigments, including most of those discussed in the guide to watercolor pigments.
The maximum hue purity or MacAdam limit was calculated from the CIE 1964 10° standard observer (Stiles & Burch colormatching functions) under an equal energy (EE) illuminant.
Unclassified mineral pigments, marketed by Daniel Smith as Primatek paints, have been included to suggest the range of moderately chromatic natural minerals that is, the range of inorganic surface colors typical of the environment to which human vision is adapted.
Each row, in order of increasing hue purity, lists:
COLOR INDEX generic C.I. name of the pigment (this is missing for convenience mixtures and unclassified mineral pigments)
All the pigments with the highest hue purity, above 70%, are confined to the orange to red hue span (pyrrole orange PO73, pyrrole scarlet PR255 or pyrrole red PR254), with the sole exception of ultramarine blue (PB29).
The scatterplot below suggests both that optimal colors can be used to further refine the CIECAM chroma estimator, and that optimal colors (physically possible colors) may define an ecologically valid stimulus limit in the adaptation of human vision (and perhaps all terrestrial animal vision).