A many times used redox titration is one with the couple: I3/S2O32-(iodine with thio sulfate).
This titration is mostly applied in an indirect titration where the investigated substance is substituted by Iodin or by thio sulfate, dependent on the question wehter that unknown substance is a reductor or an oxydator.
In this so calles 'iodometric titrations' we use a very cheap and effective indicator: starch(aq), a solution of amide.
Fresh starch has spiralshaped molecules (see also module 12, biochemistry); the tri iodide ions exactly fit and take care of a dark blue color.
The tri iodide ion itself also has a color (yellow brownish), but the disappearance or appearance of that color is less obvious than the dark blue color.