There is a set of colour truths and colour principles that can be said to comprise our colour-knowledge. It is to this body of knowledge that colour science contributes. It is possible to find some unifying order that brings together in a unitary scheme these various colour truths and principles. The set of truths and principles can be divided into separate categories, which bring out the different roles played by colours and colour-concepts in (i) the acquisition of colour terms in language; (ii) the appearances of colours (iii) the development of first-order truths or `truths' about colours and (iv) servicing social and epistemological purposes.

L: Principles about the Use of Colour Terms:
1.Colour terms are taught and learned by the use of paradigms. This is to say that the paradigms are identified and recognised by the way they look (appear).
2.Colours are properties of bodies that play a causal role in the learning of colour terms and the communication about colours.
3.Cross-cultural comparisons indicate that there are certain basic colour terms which are systematically related.
[See Berlin and Kay (1969), and Boynton and Olson (1990), and for a contrary view, Van Brakel (1993)]

A: Principles about Appearances and the Perception of Colour:
1.Specific colours have distinctive appearances, characteristic of each colour.
2.The way colours are identified and recognised is by the way they appear to perceivers. There are no colour thermometers or other measuring devices.
3.Colours take a different mode of appearance, i.e., have a different characteristic appearance, when they are features of physical surfaces, films, volumes, light sources, etc.
4.There are principles governing the conditions under which colours are perceived. Certain conditions are better than others for identifying colours; certain people are better than others at identifying colours. Coloured bodies can appear differently when viewed at different distances, in different illuminations, and against different backgrounds.
5.Among the principles in A4 are principles governing constancy effects: tendencies for objects to look the same under different conditions.
6.There is a certain distinctive form to the way colours appear. Visual experiences represent colours in a certain way, as qualitative  features which are "sensuous" in the widest sense.

T: Colour Truths of the First Order:
1.There is a vast range of specific colour truths: ripe bananas are yellow; certain sunsets are golden; claret wine is claret red and so on.
2.Colours can be combined together in structured, systematically ordered arrays, with a distinctive character. They are qualitative features which are "sensuous" in the widest sense. These arrays are different depending on whether the colours are colours of surfaces, volumes, films, scattering media, lights and so on.
3.There are general causal truths e.g., ripening pears, bananas and wheat go from green to yellow, acids turn blue litmus paper red, spiders with red stripes on the back are venomous, black hair tends to grow grey with age, and so on.
4.Different colours have different specific aesthetic effects, including principles of harmony, balance, contrast, etc.
5.Different colours have different emotional effects.

R: Principles about Colours and Their Roles:
1.Colours are natural signs, i.e., are easily identifiable features of objects that enable perceivers to identify and re-identify kinds of objects.
2.Colours serve as conventional signs, for similar purposes as those in R1.
3.Colours, often because of effects in T4 and T5, serve certain social and psychological roles.

It needs to be emphasised that these categories are not meant to be exclusive. For example, principle R3, concerning the social and psychological role of colours is related to principles T4 and T5, concerning the specific aesthetic and emotional roles of colours. Likewise the principles in A6 and T2 both refer to the sensuous nature of colours.