The white and black colour attributes in the Natural Colour System

This phenomenological research investigates how it is possible to determine the extent to which a chromatic colour appears white and black in order to use it to build a new Colour Rendering Index. We tested two methods of subjective evaluation; in the first, the perceptual presence of white (and black) in a colour alone was assessed on a unipolar intensity scale, independently for the two attributes. In the second method, evaluations of whiteness (and blackness) were conducted for colours presented in a sequence ordered from the least to the greatest presence of the respective attribute. In both tests evaluations were made either by moving an arrow on a slider from left (minimum) to right (maximum) or by choosing a grey cylinder that matched the same degree of similarity to white (and black) as the test colour. In four experiments, 16 colours of 4 hues and 4 different shades were studied; in a fifth experiment, 48 colours, 12 for each quadrant of the colour wheel, were studied; finally, in another test, 10 greys were studied. In the first three experiments, the results were unexpected, as the evaluations of whiteness and blackness were complementary, adding up to 100%, while in the current NCS, 100% includes not only the evaluation of white and black but also that of chromaticness, therefore white and black are not complementary. In the fourth and fifth experiments, the sum of the evaluations of white and black was always less than 100%, in accordance with the present NCS. In the last experiment, the evaluations of white and black given independently to the 10 greys samples were complementary, confirming the bipolar nature of white-black continuum. Suggestions have been provided to resolve the discrepancy between the results of this research and the structure of the current NCS.