achromat - person who is unable to see chromatic colour; might be inherited (rod achromat) or due to brain damage; state: achromatopsia

achromatic colour - colour lacking hue; i.e. white, grey or black

anomalous trichromat - person with three types of cones, one of which has deviant properties; needs three primary colours for admixture of all hues, although typically in non-normal proportions

blind spot - blind area enclosed within portions of the retina and visual field, exit site of the optic nerve (optic disc), hence lacking visual receptor cells

brightness - apparent intensity/amount of light in a visual percept (Plate 1.1)

chromatic colour - colours with a hue, i.e. all colours except white/grey/black; cf. achromatic colour

chromaticity - hue and level of saturation

colourfulness - relative degree of saturation or ‘purity’ of a chromatic colour (Plate 1.1)

complementary colours - pair of hues for which an additive mixture may become white; each spectral and extra-spectral hue has its own complementary colour

cones - class of receptor cells of the retina, used for photopic vision in normal daylight; three types with different wavelength sensitivity (L long, M middle, S short wavelengths); essential for seeing colours and fine detail

dark adaptation - adjustment of the sensitivity of visual receptor cells and the processing in the visual neuronal system to a decreased light intensity (e.g. from day to night)

deuteranomal - person with an inherited disturbance of red-green colour vision in which the M cones have deviant properties, state: deuteranomaly

deuteranope - person with an inherited disturbance of red-green colour vision in which the M cones are non-functional; state: deuteranopia

dichromat - person with two types of functional cones, needs only two primary colours for admixture of all hues; state: dichromacy

dominant wavelength - wavelength of spectral colour that represents the hue for an unsaturated colour; obtained using CIE charts (Figure B.1)

elementary colours - six colours perceived as ‘unique’ according to Hering's opponent colour system; four are chromatic (blue, yellow, green, red) and two achromatic (white, black)

extra-spectral colours - purple hues, do not occur in the spectrum because they cannot be produced using light of a single wavelength; made with e.g. blue + red

fovea - small retinal region for which acuity is maximal, lies at the centre of the normal gaze direction; […]