Touching, tasting, smelling, hearing, and seeing - these are the ways we get our information about the world. But the world of humans is primarily a world of sights, with 90 percent of what we know of the world coming to us through our vision [1].  What we see is colour. Colour is a visual experience, a sensation of light that cannot be verified by other senses-not by touch, taste, smell, or hearing. The eye’s retina absorbs the light sent to us from luminous objects (eg. light bulb) or reflected from a non-luminous object (eg. a table and chair) and sends a signal, or sensation, to the brain. This sensation makes us aware of a characteristic of light, which is colour. Scientifically, light (made up from photons) is just one form of visible energy while colour is simply light of different wavelengths and frequencies. The way in which most of us actually see colour, is through the sensors in the retina of our eyes called rods and cones. The rods are very sensitive to light but are mostly colour blind. The colour detectors in the eye are the cones. Each cone contains one of three pigments sensitive to RED, GREEN or BLUE. Each pigment absorbs a particular wavelength of colour eg. short wavelength cones absorb blue light, middle wavelength cones absorb green light, and long wavelength cones absorb red light.

When we observe a colour that has a wavelength between that of the primary colours red, green and blue, combinations of the cones are stimulated. The result is that we can detect light of all colours in the visible spectrum. Each colour has its own properties with its own wavelength and frequency. The human eye is able to sense wavelengths of light ranging from about 400 nm to about 700 nm. Red is the longest visible wavelength (720 nm), followed in order by orange, yellow, green, blue, indigo, and violet, the shortest visible wavelength (380 nm). ROYGBIV is an acronym for these wavelengths, which are the colours of the visible spectrum. In order for an object to be seen as a colour, the wavelengths that its colourant reflects must be present in the light source. If a red object is placed under a source that lacks the red wavelength, all light reaching the object is absorbed. No colour is reflected back to the eye. A red object is seen as black under green light [2].

Basic cross section of human eye showing rods and cones.
Source: Colour Therapy Healing, 2010.

Roses appear to be red because they contain a red pigment which absorbs most of the visible light spectrum, while reflecting mainly red back to the viewer.
Source (dancer): by Sanjana Reddy http://www.vogue.in

The position of the light source will determine the angle in which the light will reach the object while the direction of the reflected light beam will influence how colours are perceived in terms of its lightness and darkness.

Display of density models at Venice Architectural Biennale 2006:
Photo: Shruti Hemani

Transparent, Translucent, Opaque Wine Glasses:
Source: Google

Water colour painting by Shruti Hemani, 2006. Women assembly, Rajasthan.

Watercolour  is described  as a  luminous  medium  because light  reaches through the colourant of the white of the paper and created coloured effects on the paper. Watercolour on black paper is not luminous, because no light reflects from the black paper surface.

The Science of Colour Theories: [3]
It is the light that generates colours. Without it there is no colour. The sun, a fundamental source of light, is sensed as white (or colourless) but it is made up of mixture of colours which can be seen by passing the sunlight through a prism. There are two theories that explain how colours work and interact. The light or additive theory deals with radiated and filtered light. The pigment or subtractive theory deals with how white light is absorbed and reflected off of coloured surfaces.

• Light Theory:
Light theory starts with black (the absence of light). When all of the frequencies of visible light are radiated together the result is white (sun) light. The colour interaction is diagramed using a colour wheel with red, green and blue as primary colours (Red, Green and Blue). These are the three colours that the cones in the eye sense. This is an RGB colour system. The primary colours mix to make secondary colours: red and green make yellow, red and blue make magenta and green and blue make cyan. All three together add up to make white light. That is why the theory is called additive.

A computer monitor or a coloured television is an example of light theory. The same three primary colours are used and mixed by the eye to produce the range of colours you see on the screen. This theory is also used for dramatic lighting effects on stage in a theatre.

• Pigment Theory:
Pigments behave almost the opposite of light. With pigments a black surface absorbs most of the light, making it look black. A white surface reflects most of the (white) light making it look white. A coloured pigment, red for instance, absorbs most of the frequencies of light that are not red, reflecting only the red light frequency. Because all colours other than the pigment colours are absorbed, this is also called the subtractive colour theory. If most of the red light is reflected the red will be bright. If only a little is reflected along with some of the other colours the red will be dull. A light colour results from lots of white light and only a little colour reflected. A dark colour is the result of very little light and colour reflected.

The primary colours in the pigment theory have varied throughout the centuries but now cyan, magenta and yellow are increasingly being used. These are the primary colours of ink, along with black, that are used in the printing industry. This is a CMYK colour system [Cyan, Magenta, Yellow and (K) black].

Light Effects:
• Opaque, Translucent and Transparent:
If all the light reaching the object is transmitted, the object is transparent eg. Clear glass. When the light reaching the object is partly reflected and partly absorbed, the object is translucent eg. Butter paper or tracing paper. If all the light reaching an object is either reflected or absorbed, the object is opaque eg. Ceramic teapot.

• Luminosity:
Luminosity is the attribute of emitting light without heat. A luminious object is light reflective but does not emit heat.

• Indirect Light/Colour:
An indirect colour is the variant of indirect light. An indirect colour occurs when a light reaches a highly reflective colour on a broad surface and reflects onto the nearby object which changes its apparent colour due to the reflect light /colour. 

Scattering:
The position of the light source will determine the angle in which the light will reach the object while the direction of the reflected light beam will influence how colours are perceived in terms of its lightness and darkness. Different textured surface does not affect the actual colour (wavelength) of the light but a smooth surface will reflect more light directly than a matt or rough surface which reflects light in a more fragmented way. Hence the smooth surface may appear lighter and brighter than a rough surface. Heavily textured or irregular surfaces scatter light is many directions and can created light-dark variations of colours that make it dynamic and lively. Varying textures of surface allows designers to create such effects when their scope is limited to only one colour or material. Emboss materials or frosted glassware create patterns with single colour or material [2].

[1] Miller, H. Experience of Colour, http://www.hermanmiller.com/
[2] Holtzschue, L. (2011) Understanding Colour:An Introduction for Designers, John Wiley Sons.
[3] The Science of Colour Theory developed from Jim Saw’s Art 104: Design and Composition, Palomar College, 2012), http://daphne.palomar.edu/design/color.html, 2011