Colour Theory Basics

Colour Dimensions

• Colour dimensions are the attributes used to judge an object's appearance, such as red, orange, yellow, green, blue, and purple.
• These colours are found on a basic colour wheel or a simple box of crayons and are placed on a continuous, circular scale.

Hue

• Hue is the attribute that enables the distinction and differentiation among different colours.
• Hue is judged by the colour's appearance, such as red, orange, yellow, green, blue, and purple.

Value

• Value refers to the lightness of a colour.
• It is the achromatic vertical scale from black to white, representing all shades of gray.
• Value is usually communicated in terms of lighter or darker.

Chroma

• Chroma is related to the variation in strength of the same colour.
• The further away from the achromatic vertical axis, the higher the chroma (stronger, more intense).
• The closer the colour is to the achromatic (value) axis, the lower the chroma (paler, weaker).
• Chroma is often described as more chromatic or less chromatic.

Munsell Colour System

• The Munsell colour system is a three-dimensional model that forms the basis for the classification of coloured objects in the three dimensions: hue, value, and chroma.
• The system was devised by American artist Alfred H. Munsell in 1898.

Other Optical Properties

• Translucency is the degree to which an object scatters light upon transmission, resulting in an appearance between complete opacity and complete transparency.
• Iridescence is a rainbow-like effect caused by the diffraction of light that changes according to the angle from which it is viewed or the angle of incidence of the light source.
• Chromatic induction is an illusory sensation of colour created when two objects of the same colour are surrounded by different coloured backgrounds.
• Chromatic induction can generate either a contrast effect or an assimilation effect.
• Blending effect is a perceptual phenomenon where a restorative material (object) takes on the colour of the tooth (background/surround) and appears more similar combined than when viewed in isolation.

Colour Perception

• Colour is interpreted by the brain after the neural signals are transported by the optic nerve.
• There are three types of cones in the retina that are sensitive to different wavelengths of light: blue, green, and red.
• The blue cones are most responsive to short wavelengths, while the green and red cones are most responsive to medium and longer wavelengths, respectively.

Colour Deficiency

• Colour vision deficiency is a weakness or absence in one or more of the three types of cones.
• Individuals with colour deficiencies still see colour, but their colour vision is distorted.
• The most common colour deficiency is an individual with a partial green defect known as deuteranomaly.
• Colour deficiency poses a challenge for the clinician when performing visual shade matching.
• Popular general tests to check colour vision are the Ishihara test and the Farnsworth–Munsell test.