Term: colour indicator
https://doi.org/10.1351/goldbook.C01180

Definition:
An indicator which is classified as one- or two-colour, depending on whether it is colourless on one side of the transition interval or possesses a different colour on each side of this range.

Source: Orange Book, 2nd ed., p. 48 (https://media.iupac.org/publications/analytical_compendium/)

Citation: 'colour indicator' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.C01180

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