There are two types of cells in the retina of our eye that are responsible for our perception of colour: rods and cones. Cones, which are sensitive to colour, function best in bright light. They exist in three forms, each differing in the wavelength of light absorbed (LMS). Rods, on the other hand, are sensitive to the intensity of light. In the human eye, rod cells allow us to distinguish and detect objects in the dark; however, since their sensitivity to light is better than cone cells, our ability to perceive the colour of objects in an area of low light becomes poor.
Colour perception requires light. When light strikes objects, some are absorbed and some are reflected. The resulting colour seen by the viewer is due to the reflected wavelengths. Wavelengths that can be seen by the human eye belong to the visible light portion of the electromagnetic spectrum. The colours range from short wavelengths to long wavelengths, starting with purple, followed by blue, green, yellow, orange and ending with red.
Since there are slight biological variations between people, the way we perceive colours and recognise colours will vary, too. Hence, determining an object’s colour becomes subjective. For example, take this box below, some may refer to its colour as blue, some may say it appears green and for the colour-critical person, they may say cyan. To provide an accurate description of an object’s colour would be highly impossible for the average individual.
We must rely on quantitative methods to accurately communicate and document an object’s colour. Colour space is the term we use to collectively define the range of colours that is displayed on monitors, produced by printers, or that can be captured by cameras, to name a few. Commonly used colour spaces include RGB, CMYK, HSV, CIEXYZ, CIEL*a*b*.
True colour, then, is an accurate colour representation of the original image in reality.