Redox indicator

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.
There are two common classes of redox indicators:
The most common redox indicator are organic compounds.
Redox Indicator example:
The molecule 2,2'- Bipyridine is a redox Indicator. In solution,it changes from light blue to red at an electrode potential of 0.97 V.