Why is no external indicator needed when titrating iron (II) with potassium permanganate?

Potassium permanganate solution is intensely purple. During the titration, it is reduced to nearly colorless $\text{Mn}^{2+}$ ions. Once all the iron (II) ions have reacted, the first drop of excess potassium permanganate solution will cause the solution to turn a persistent pale pink color, indicating the endpoint of the titration.