Colour and dimensions
Everyone is aware of the three dimensions of space – length, width (or depth) and height, which are typically expressed in graphs as three mutually perpendicular axes – x, y and z, representing relative positions involving movement from side to side (left (-x) and right (+x)), from above and below (up (+y) and down (-y)) and from front to back (forward (+z) and backward (-z)). Often on paper there are only two dimensions expressed – x and y, representing positions involving movement from side to side and from up to down only.
Modern educated people will also be aware there is a fourth dimension in physics called time from past to future (backward (-w) and forward (+w)) which is sometimes plotted on paper as one of two or three dimensions, eg a 2D plot of growth against time, where the w axis is normally called the x axis.
However, there are many more properties of things which can be measured and called dimensions. Colour is the most powerful of these and therefore the most useful. Colour is actually multi-dimensional, because in addition to the effective hue, and there are lots of them, including red, yellow, green, blue, white and black, it has intensity, lightness or brightness on a scale from black to white, giving shades of each colour, including grey, which is a light shade of black.
Colour production and measurement
There are several ways of producing colour depending on the media involved. Different combinations of red, green and blue transmitted light produce different colours on TVs, monitors and film. Different combinations of red, yellow and blue reflected light from paints and stains, assisted by black and white paints, produce different colours on paper or other solid matter like canvas or timber. Different combinations of cyan, magenta, yellow and black inks produce different colours on paper in printers.
There are different ways of measuring colour, but they can be grouped as additive or subtractive procedures and commonly involve measuring three or four properties of the light. Visible light wavelengths for humans ranges from low frequencies 430 THz (430 x 1012 Hz) for purples to high frequencies 790 THz for reds.
In the RGB additive system the relative percentages of the red, green and blue coloured lights are measured and if used together in the right proportions they produce white. In another additive system, measurement involves scores on the red-green axis of a colour sphere space, scores on the blue-yellow axis of the space and the brightness scores on the black-white axis, which again give white with the right proportions. Another additive example named after Munsell scores brightness on the black-white axis of a sphere, chroma or colour purity score around the circumference and intensity as the score along the radius from the black-white axis to the actual colour, again producing white in the appropriate proportions.
The CMYB system is a subtractive system where cyan, magenta, yellow and black are subtracted from the white colour of the paper to produce reflected colours ranging from white through any of the colours to black in the extreme.
Use of colour in graphics
So, it is common practice to plot not only in x, y, possibly z (and perhaps w), but to use colour to differentiate between different treatments, scenarios and effects involved in the process. A diagram without colour, even if shading, stippling and hashing are employed and dotted, dashed and other fancy lines are used, is vastly inferior to a coloured diagram. The only disadvantage in using colour in presentations, reports, etc is the cost which may be double or perhaps up to quadruple the price of the corresponding illustrations depicted only in black, white and shades of grey.
In the 21st century, I believe colour should be used wherever possible. Even club newsletters these days contain coloured photographs and coloured text, including fancy fonts. My book ‘Is Your Picture Worth a Thousand Words?’ emphasises the value of colour in helping considerably to quickly and easily impart information to readers or audiences, effectively enhancing comprehension of the information in presentations, reports and other material.