Title: Colors

Source: Ekman (1963)

Description: Six monochromatic lights of equal brightness served as
stimuli. Their wavelengths were 593, 600, 610, 628, 651, and 674 nm,
i.e., the lights were in the red-yellow range. All possible pairs of
lights were projected onto a screen, and ten subjects were asked for
"contained-in" judgments on each pair. The averages of the observed
values are presented in the table.