Pink or purple can be a sign of a few different things, based on the type of film being used and your developing process. It can be a sign of under-fixing your negatives; this should be ruled out first. Make sure you used fresh fixer of the proper dilution, at the proper temperature, for the proper time. If any of this is in doubt, refix immediately, then wash and dry as normal.

Note: The reverse is not true – you cannot use the lack of dye color as an indication of proper fixing.

If this doesn’t resolve the issue, then you probably have a sensitizing dye in your film that didn’t wash out. You can safely ignore this dye if you wish, as it will not affect the life of the film or its use in printing. If you wish to remove this dye, try the following:

- Wash for a longer period. The amount of time that the film spends wet seems to have an effect, and the dye may wash out. Wash water at 80ºF / 27ºC may also help.
- Fix for a longer period of time. This is especially the case with some Kodak films, which require a longer fixing time. An alkaline fix will help with this as well.
- Use a sulfite-based hypo clearing agent / wash aid after fixing.

If you want to remove the stain after the film has been dried, try one of the following:

- Immerse your negatives into a bath of 1% sodium sulfite and agitate them until the color is gone from the film. Wash and dry as normal.
- Expose the film to UV light, such as sunlight, for 1-5 hours. This may remove the color, although some question if this might harm the negative as well.

Note: This is my summary of the thread here - Pink or Magenta Cast with T-max, new Tri-X, and other films (not blue or green cast)