The Colour Guide
Contributor: Mike de Sousa, Director, AbleStable®

Colour is a far more difficult medium to interpret than at first meets the eye.

Sighted people may assume they have a clear notion of the colour red, but ask a group of ten individuals to choose from the reds below and there's little consensus about what might be 'pure red'.

This guide provides the reader with essential knowledge about light and colour. The better informed we become about colour, the more effectively we can appreciate it's subtleties, and manipulate its nature.

Light

Light is part of a range of vibration energies called the 'electromagnetic spectrum' which includes gamma and radio waves. For most people whose sight functions effectively, the retina at the back of their eyes receives and responds to light energy.

Natural white light is a mixture of the visible bandwidth which runs from around 380 nanometres (the limits of violet), to about 760nm (the limits of red). A nanometre (nm) is a thousandth of a millionth of a metre: 1/1,000,000,000 of a metre.

Light is unique in having properties of both particles and waves. Light particles (photons) radiate from their source in a wave pattern at a constant speed. Like waves in the sea, light waves have a crest and a trough.

Light travels at great speed and is the the fastest medium we know of: 299,792.458 km/s (186,000 miles per second).


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Colour

Light is energy, and colour is a product of the interaction of that energy and matter. However, seeing colour is not only dependant on the nature and interaction of light, but also on our physiological, and psychological response. The perception of light and colour is therefore ultimately a personal experience that is never exactly the same between any two people.

When a beam of light is shone through a glass prism, or you observe a rainbow in the sky, the order of the colours is always the same:

Violet, Indigo, Blue, Green, Yellow, Orange, and Red.

The colours we see is what light remains of the spectrum after part of it is absorbed. In the case of the example above, some light is reflected and some absorbed by a gray surface.

Black is perceived when all light is absorbed. White is perceived when all light is reflected (pigment), or all colours are present (unreflected 'transmitted light').

To gain an understanding of light it is important to make the distinction between how transmitted light reaches our eyes (light produced by the sun, a fire, a light bulb etc), and how reflected light reaches our eyes (light reflected off the surface of an object).


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Colour Terms

Various methods are used to classify colours in an attempt to help us understand and select colour. However, different authors use different terms to describe the same concepts. Some attempt to distinguish between light emissions and pigmentary reflection by using different sets of terms.

The most elegant method seems to be to classify colours in one of three ways: by hue, brightness, and Intensity.


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Hue

Hue is a term that is widely used but generally misunderstood.

Hue can be defined as different visible wavelengths. A hue is the principle difference caused by separating the wavelengths of white light (white light is made up of all the visible wavelengths). Put another way: hue is the visible differences between pure colours. The pure colours are: red, orange, yellow, green, blue, indigo, and violet. Hues make up all the colours inbetween. Hue therefore is a problematic term, as we each perceive a 'pure colour' differently.



Companies like Pantone attempt to act as authorities on colour classification, but there are also inherent difficulties in this endeavour. A significant issue that arises is the deterioration of pigments. The moment a pigment is exposed to light, a chemical process begins that alters the colour.

Pantone generates a healthy income by producing colour reference materials, software, publications, and hardware products that provide fresh pigment referencing year on year. The colour charts, swatch cards, and books however should be replaced regularly for an accurate colour match as the reference materials themselves deteriorate. Choosing a colour using an old colour reference will not produce exactly the same colour as the paint manufacturer produces, and causes potential colour mismatching.

Another problematic issue are the differences that exist between TV and computer monitors. Companies like 'E-Color' produce software to assist with consistent colour optimisation which is an important issue when selecting goods over the Internet where colour is a consideration.

Any standardisation system is however flawed because we perceive colour differently.


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Brightness

Brightness: the range from light to dark. A gray scale is a range of visible light from white to black, but also includes a range from any light colour to any dark colour. OK, I can get to grips with that one :-)



Brightness may also be known as 'illuminosity', or 'brilliance' when used in the context of transmitted light as opposed to pigment.


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Intensity

Intensity: the range of any pure hue to any point of gray scale.



There are a number of terms which are also used when speaking about visible intensity:

• Tint: the range from a pure hue to white.

• Shade: the range from a pure hue to black.

• Tone: the range of a pure hue to any gray.


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Primary Colours

An important principle to understand is that pigments (paints, chalks, pastels etc) are mixed in a different way to transmitted light. When coloured light beams are projected onto a screen, the areas of overlap are called 'additive mixtures'. Overprinting transparent colours like paints results in 'subtractive mixtures'.

Additive mixing is so called because each new superimposed colour adds to the brightness of the mixture. In subtractive mixing, each new superimposed colour reduces the brightness of the mixture. To confuse matters, using a computer software 'paint' program on a monitor follows the subtractive model, even though the monitor is actually transmitting light. Graphics software is generally produced to model its behaviour as if the light materials (colour) are pigments.

Primary Colours (pigment)

Children are generally taught that there are three primary colours: red, yellow, and blue. These colours can produce a broad range of hues, however the primary colours used in commercial printing are magenta, yellow, and cyan. It is magenta, yellow, and cyan that can effectively produce all other hues by mixing them. Black is often also added to create a 'four colour' printing process known as CMYK.

Secondary Colours (pigment)

Mixing two primary colours produces a 'secondary colour' (sometimes known as an intermediate colour).

Primary Colours (light)

The three primary colours used in an additive method are: red, green, and violet.

Secondary Colours (light)

It is interesting to note that the three secondary colours used in an additive method are magenta, yellow, and cyan (the same primary colours used in the printing process).


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Colour Values

Examples of the most common ways of classifying colour value follow:

RGB

Values of Red, Green, and Blue, where each component has a value from 0 to 255. 0-0-0 is black and 255-255-255 is white.

Hexadecimal RGB

Values of Red, Green, and Blue, where each component has a hexadecimal value from 00 to FF. 00-00-00 is black and FF-FF-FF is white.

HSB

Values of Hue, Saturation, and Brightness, where Hue has a value from 0 to 360 degrees, and Saturation and Brightness have a value from 0 to 100%.

CMYK

Values of Cyan, Magenta, and Yellow, where each component has a value from 0 to 255. 0-0-0 is white and 255-255-255 is black.

Grayscale

A percentage of black. The single Black (K) component has a value from 0 to 100%, where 0 is white and 100 is black, and in between are shades of gray.


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Choosing Colours

There are several 'tools' that can assist in the process of organising and choosing colour, however it is important not to be simplistic about the choices available, or dogmatic about the colours that 'compliment' one another. An example of a tool that attempts to help with our choice of colour is the 'complimentary' colour wheel.

The Colour Wheel A colour wheel describes the relationships between colours. It is most often laid out so that the additive primary colours P (red, yellow, blue) are separated by secondary colours S (orange, violet, and green), and tertiary colours T (turquoise, lime, cyan, purple, ruby, and magenta). As has been discussed earlier, the primary colours differ from those used in the print industry.