Introduction

Colours spur us to philosophise. Colours are so familiar that we cannot help wondering why they can be troublesome and enigmatic for philosophers. They have been subject to much discussion in the history of philosophy: from Aristotle's remarks on exclusions by contrariety and problems for the Principle of Excluded Middle to the collapse of Wittgenstein's early Philosophy; from Locke's discussion of secondary qualities to puzzles about perception relevant to the so-called Hard Problem of Consciousness; from the debate about synthetic a priori truths to challenges for the possibility of sharp distinction between shape and content in aesthetics; from issues with the distinction between the subjective and the objective to technical efforts to pin down the irreducible element of vagueness in our language; from ontological discussions and thought experiments to experimentation in neuroscience concerning perception and cognition. In all these examples, colours occupy the centre of the discussion by illustrating difficulties or the very path for solutions.

Accordingly, colours pose problems and challenges to theories of perception, of rule-following and classical principles of logic. They serve as illustrations of harmonic and holistic systems. Colours encourage intricate models in linguistics and mathematics. They also represent common ground for the Gestalt tradition as well as puzzles for some central accounts in the philosophy of mind. Indeed, colours are a favoured example in many central philosophical arguments where they are used systematically in support of some theses and as counter-examples to refute others. Discussions about the nature of colours reside at the core of many classic disputes in metaphysics and epistemology, such as those between Locke and Leibniz, Newton and Goethe, as well as Wittgenstein and himself.

A good example of the importance of colours for philosophy can be seen in Wittgenstein's philosophical development. It seems there is no end to the examination and discussion of the various and seminal ways in which colours matter in Wittgenstein's philosophy. Throughout his philosophical career, the theme of colour was one to which he returned constantly. His active reflections on colour appear already in crucial passages in his first work, Tractatus Logico-Philosophicus. Further, one of the unfinished manuscripts discovered in Cambridge at the time of Wittgenstein's death (1951) was triggered by Goethe's seminal but controversial work on colour, and was published posthumously as Remarks on Colours (1977).