I used the phone yesterday and some water from my towel wrapped hair managed to seep inside my iPhone. It became discoloured and it drove me up the wall. I fixed it. There is a solution if you have this issue.
Get a plastic food bag or Ziplock bag and place raw rice inside. Go to your settings and select brightness/wall paper and select “never” on autolock. Then turn your brightness all the way and submerge the phone in the bag with the rice. DO NOT DO THIS WITH THE CHARGER PLUGGED IN THE PHONE! Just the phone itself. Do it overnight for a few days. The next day you see a difference. Anyway, the shit works. The stains start to vanish over time. You do see immediate results.