Colour may be produced by one or more of the following:

1) Colour produced by interference or diffraction phenomena.

2) By scattering and dispersion phenomena.

3) Colour production by emission process.

4) Colour production by selective absorption of particular wavelengths in white light.

The colours in soap bubbles, oil on water and Mother of Pearl are all produced from interference and diffraction phenomena.

The sky appears blue, sunset turns the sky red) eyes appear blue or brown, all due to the scattering effect of particles in that media.

Colour television, fireflies, candles, sodium streetlights are examples of emission sources.

Selective absorption allows us to see colour:

Grass appears green because of preferential absorption of red light

Blood       "         red          "                      "            “green   “

Jeans        “        blue         “                      “            “orange “

Oranges   "        orange     "                      "            ” blue    “

Grass absorbs red light, leaving yellow, green, blue and violet. The combination of these colours appears green. The colour with maximum absorption results in the colour opposite within the colour circle being transmitted.

The distance between atoms in a molecule and the energy levels holding them together may be of sufficient energy that they are able to absorb selected frequencies of radiation, e.g. different parts of the body absorb different amounts of X-Rays, allowing us to differentiate bones and skin.

Similarly, some chemical compounds will absorb radiation within the wavelengths of the visible spectrum. If we consider a compound which absorbs in the whole visible spectrum, so none of the light is reflected back, what we see, there is no light, so we see black. Similarly, a compound which does not absorb in the visible Spectrum reflects back all frequencies and is seen as white.

Try measuring the temperature on a sunny day of a black and white car, the black one may be 10-20°C hotter, the absorbed colour (radiation) is dissipated as heat.

Now that we have established how pigments work, by absorbing part of the light and reflecting the rest, it becomes easier to understand the importance of the type of light we use for matching colours. In order to see a colour as it should be, the light the colour is viewed under must be uniform across whole of the visible spectrum. The Refinisher‘s worst enemy in this area is probably the low pressure sodium street light. If you look at one of these through a filter which is shaded to show all the colours of the spectrum, all you will see will be two very narrow yellow lines. This means that the street lamp is only giving out yellow light, so unless the 'colour' of your object (i.e. the colour of the light which it reflects) coincides exactly with the light emitted by the street lamp, the 'colour’ of your object will be greatly distorted.

It may well be possible to match a given colour using two different pigmentations, such that the overall reflectances are similar enough to convince the eye they are the same. The individual pigments used can have quite different characteristics, though, and this will show up under different lighting conditions. (A local repair on. for example, a red car which is an ‘A’ match in daylight may look brown under sodium lighting while the rest of the vehicle looks orange.)

This phenomenon is called metamerism.