Monochromatic unique green (UG) is more variable across the population than any other unique hue. Some researchers have reported that this broad distribution of UG settings is bimodal and that the distribution results from the superposition of two or more subpopulations. We have investigated this claim using a Wright colorimeter to measure the unique green wavelength of 58 participants and we have analyzed previous unique green literature by applying a rigorous statistical test to historical datasets. We have also explored the possibility that individual differences in macular pigment density may be responsible for the variation in unique green wavelength. Our results indicate that unique green wavelengths in our population are distributed unimodally and are correlated positively with macular pigment density; individuals with a higher density of macular pigment select longer wavelengths of light as unique green than individuals with a lower density of macular pigment. We model this effect using simulations of monochromatic unique green matching to broadband illuminations and show that matches in the region at approximately 500 nm exhibit particularly high variance both with respect to macular pigment density and also with respect to the precise shape of the broadband reference exemplar spectrum.
Keywords: bimodal; macular pigment; modeling; unimodal; unique green; unique hue.