It is essential to properly define the notion of colour. Matter itself does not have colour, it only has the property of reflecting certain light rays to which the eye is sensitive to a greater or lesser degree. Colour is therefore the visual sensation perceived by the observer of an object under a given lighting.
Different factors are involved in the perception of colour:
• Light: light is an electromagnetic wave, which can in particular be characterised by its wavelength and therefore its energy. It can considerably modify the perception of colour.
• Matter: matter has the property of reflecting luminous energy to a greater or lesser extent.
• The eye: the eye plays the role of converting the information it receives and transmitting it to the brain for interpretation.
The human eye is sensitive to electromagnetic radiation with wavelengths between 400 and 700 mm (visible spectrum). Colorimetry is the technical means of expressing a colour in mathematical terms so as to position it within a defined space, calculating the differences between a standard and a sample, determining the acceptable colorimetric tolerances and even making colour formulations.