The history of colour is long and complex. All of antiquity has played a part in the multi facets of its story. Colour straddles the scope of human culture science art and religion The Egyptians as far back as the 8th millennium used colour for healing, the Greek, Alcmaeon of Croton as early as 5th century BC recorded in his poetry the effects of colour and Romans, architect Vitruvius, refers to the mining of earth colours and the senator Seneca used the term in the 1st century. Just to give a broad brush of the vastness of colours intrigue across culture.
In the west we are influenced by the Newtonian Op-ticks.
Isaac Newton in the 17th/18th century deduced that sunlight is made up of the ‘spectrum’, a term referring to the components of white light. The components of sunlight can be seen when its wave length is separated (through refraction) by a glass prism. The result is a rainbow with ‘seven’ colours, red, orange, yellow, green, blue, indigo and violet. A rainbow in the sky after rain is the result of sunlight refracting through the particles of water drops this is when we see colour in sunlight. The seven colours are divided into two categories; the red yellow and blue are called primary colours. The orange, purple and green are called secondaries/opposites/complementary.
If we join the spectrum at one end to form a circle we will have made a colour wheel. Red will be opposite to green, blue to orange, yellow to violet. These colours are complementary to one another. When placed next to one another they serve to heighten the intensity of each colour, causing an optical effect of vibration. The impressionists used this method to great effect in a distinctive revolutionary way much like pixels in digital photography today (We can talk about this at length in another insight).
The components of shadows, contain this same principal but mixed together, that is the main colour of the object, using just the primary/secondary colours, (no white) red, yellow or blue, green, purple, orange, say the vase is greenish/blue, more blue than yellow (this is the pure colour of the vase) now add the opposite on the colour wheel this being red/orange. This is now the colour of the shadow on the greenish/blue vase.
The Colour Wheel as Demonstrated. The colours Red, blue, and yellow are primary colours which when mixed together, make all other colours. These colours cannot be made they are mined as raw material.
Secondary Colours. Complementary colours or opposite colours. By mixing two of the three primary colours together we get the opposite or complementary colour of that colour which is left, for example, take two of the primary colours red and blue mixed together this makes purple and the remaining primary colour is yellow therefore yellow is the opposite of purple. The other secondary colours are red and yellow mixed together makes orange; the opposite is the remaining primary colour which is blue. Also yellow and blue mixed together makes green and the remaining colour is red therefore the opposite of green is red.
A Demonstration of the Spectrum Appearing out of White Light
Enlarge the black and white wheel to see the spectrum come out of white light. Focusing the eyes on the centre of the wheel produces the rainbow spectrum.
Demonstration of Opposite Colour
Place a piece of reasonably strong coloured paper on a white piece of paper, under intense light, stay focused for 30 seconds, either close the eyes of continue to stare at it. When closing the eye you will see an after image of the opposite colour, if you keep the eyes open and focused on the piece of paper, a halo will appear around the piece of paper.