First off, no one should be intentionally submerging their phones in water. Yeah it's safe to use in the rain but that's about as far as I would take it. I see the IP67 rating as a safety feature - my car has airbags but I'm not going to go driving into walls to make sure they work.
With that being said, I doubt you'll see anyone with a pink water indicator as there is a rubber gasket/seal around the SIM card tray. It's a pretty decent guarantee that no water will enter the tray when using the iPhone in the rain. It would take a relatively decent amount of water pressure (i.e. being submerged more than 3 feet) for water to enter the tray. With that being said, always make sure your SIM tray is seated very well into its slot!