Full Idea
On Sainsbury's picture, a colour has an extension that it has by virtue of its place in a network of contrary colour classifications. Something is determined to be 'red' by being a colour incompatible with orange, yellow, green, blue, indigo and violet.
Gist of Idea
The extension of a colour is decided by a concept's place in a network of contraries
Source
Ian Rumfitt (The Boundary Stones of Thought [2015], 8.5)
Book Reference
Rumfitt,Ian: 'The Boundary Stones of Thought' [OUP 2015], p.245
A Reaction
Along with Idea 18839, this gives quite a nice account of vagueness, by requiring a foil to the vague predicate, and using the disjunction of the predicate and its foil to handle anything caught in between them.
Related Ideas
Idea 608 There is no middle ground in contradiction, but there is in contrariety [Aristotle]
Idea 18839 An object that is not clearly red or orange can still be red-or-orange, which sweeps up problem cases [Rumfitt]