The degree to which people can discern differences in hue on a computer screen was explored in this study. A purpose-written program offered participants a colour swatch and a nearby panel to be matched by adjusting its hue by mouse or keyboard. Offered colours were defined with randomly-chosen values of R, G and B (red, green and blue values as the computer colour definition); and the lightness and saturation of the matching swatch were maintained at the values of the offered swatch while the participant attempted to match the hue. The test was taken by 329 participants from five geographic locations, yielding more than 14 000 colour matches, and answers to 10 questions about their intrinsic and extrinsic sociocultural characteristics. It was found that typical hue discrimination averaged about 223 (distinguishable hues around the HSL hue circle). Discrimination (D) varied strongly at different hues, and peaked in the orange (at D = 370) and blue (D = 330), and was lowest in the red-magenta (D = 111) and cyangreen (D = 120). Thus at some parts of the hue circle, participants could, on average, distinguish more than 3 times as many hues in a given numerical hue range as at other parts of the hue circle. The average direction of hue matching errors was much smaller than the size of errors, but was negative overall (i.e. participants tended to match counterclockwise of the offered colour). Between yellow and cyan-blue, matches were biased towards the green and appeared to be an artefact of the poor discrimination in the green. Female participants had better discrimination than males, and this was especially marked in the magenta-red to yellow-green, but also in the cyan to magenta. Young participants had better discrimination than older participants, and discrimination fell from about 35 years onwards, although decline in discrimination appeared to be less for yellow hues. Differences in discrimination were found between participants living in different environments. Living in an environment with a subdued colour palette was associated with elevated discrimination — the difference (ΔD) being +28 Discrimination units relative to participants living in a location with a flamboyant palette; the difference was especially marked in the cyan to blue hue segment. A similar difference was found for temperate vs more tropical locations where the former showed elevated discrimination (ΔD = +66) and, although superior at all hues, the greater discrimination peaked in the green to cyan. These geographic differences in effect of location were better explained by current location than origin, indicating a considerable degree of plasticity in discrimination in response to environmental influences. Similar effects were found for the effect of broad cultural milieu (Eastern < Western, ΔD = –38) and postgraduate education. Weak effects of field of specialisation and experience working with colour were also found. The key finding here is that the HSL hue circle is far from perceptually uniform, and comparison with the NCS and Munsell hue circles revealed that, despite their foundation in observed colour differences, they too, appear to be perceptually anisomorphic.