A redox indicator (also called an oxidation-reduction indicator) is an indicator which undergoes a definite color change at a specific electrode potential.
The requirement for fast and reversible color change means that the oxidation-reduction equilibrium for an indicator redox system needs to be established very quickly.
Therefore, only a few classes of organic redox systems can be used for indicator purposes.
[1] There are two common classes of redox indicators: The most common redox indicator are organic compounds.
In solution, it changes from light blue to red at an electrode potential of 0.97 V. at pH=0 at pH=7 Oxidized form Reduced form or Sodium 2,6-Dichlorophenol-indophenol (syn.