In presence of a reducing agent, MnO4−acts as a self-indicator its and end point is pink to colourless. This is because in MnO4−,Mn is in +7 oxidation state and is in highest oxidation state. Thus, will tends to get reduced and easily takes electrons and being a charge transfer (CT) complex, shows intense colour. After titration, it is MnO2 in +4 state and has no electronic charge transfer, therefore colourless.