An organic molecule that has reduced and oxidized forms with different colors; interconversion of the reduced and oxidized forms of the indicator must be reversible. Ferroin is an example.
REDOX INDICATOR (OXIDATION-REDUCTION INDICATOR)
Meaning of REDOX INDICATOR (OXIDATION-REDUCTION INDICATOR) in English
General chemistry English glossary. Английский глоссарий общей химии. 2012