achromatopsia - The complete lack of colour perception. caused by a lack of functioning cones in the eye. In "colour normals" the cones fill the fovea in the retina with information which allows the perception of fine detail and colour.

epistemology - A major branch of philosophy that concerns the forms, nature, and preconditions of knowledge.

ontology - Ontology is the study of what there is, an inventory of what exists. An ontological commitment is a commitment to an existence claim.

consciousness - Self-awareness. Subjective experience. The way things seem to us. Immediate phenomenological properties.

qualia - The 'what it's like' character of mental states. The way it feels to have mental states such as pain, seeing red, smelling a rose, etc

knowledge argument - An argument from Frank Jackson (1982) purporting to show that physicalism is false on the ground that there exist facts that cannot be known solely in virtue of knowing all the physical facts.

physicalism - The view that everything that is real is, in some sense, really physical. As used in the philosophy of science, physicalism is the view that all factual knowledge can be formulated as a statement about physical objects and activities. There is a lot of confusion in the philosophy of mind literature stemming from a tendency to take physicalism and materialism to be interchangeable.

metamers - In the case of physical surfaces there are metamers, i.e objects with very different reflectance curves that have identical appearances of colour. The situation is far more pronounced in the case of film colours or aperture colours. Here there are innumerable different combinations of light that will give the same hue. It would seem that the property shared by physical objects with the same film colour is a disposition to incite the three light-sensitive cones in the retinae according to the same ratio: x: y: z.

brightness: attribute of a visual sensation according to which an area appears to exhibit more or less light.

hue: attribute of a visual sensation according to which an area appears to be similar to one, or proportions of two, of the perceived colours red, yellow, green, and blue.

colourfulness: attribute of a visual sensation according to which an area appears to exhibit more or less of its hue.

CIE: Commission Internationale de l'Eclairage which is the french title of the international commission on light. In 1931 the CIE developed a system for specifying colour stimuli using tristimulus values for three imaginary primaries. The basis of this system was the CIE 1931 standard observer.

Tristimulus values: Tristimulus values are the amounts of three primaries that specify a colour stimulus. The CIE 1931 tristimulus values are called X, Y, and Z.

Colour constancy: the phenomenon that most colour surfaces appear to retain their approximate daylight appearance even when viewed under light sources that differ markedly from daylight. Colour constancy is surprising since the spectral distribution of light entering the eye from a surface can vary markedly from one light source to another. The phenomenon of colour constancy is only approximate, however, and surfaces do not retain their daylight colours when viewed under certain fluorescent light sources or when viewed under monochromatic radiation. Certain surfaces appear to change markedly from one light source to another and such surfaces are said to lack colour constancy; this phenomenon must not be confused with metamerism which is a phenomenon associated with at least two samples.