I've had 2 solid white cats and both had a "dirty" gray spot on their head right between their ears. It faded before they were both a year old.
Just because the cat is all white does not mean it is deaf, particularly if it had some color when it was young. So these people may very well have had an all-white cat that was NOT deaf. Some cats are just noisy.
@segelkatt The first all white cat I met was at the home of an elderly couple I was doing some work for. The cat was about 6 years old and very pretty, but Ugh she was noisy!!! She meowled and meowled almost the whole time, and no volume control. I figure she could feel vibration but as she didn't hear she had no idea how loud she was. LoL. The couple were amazing with her and took great care to make sure she didn't get out by accident as they lived beside a very busy road.
@lilla How is Hans doing? Has he returned to his lovely clean fur colour, and even more importantly, has he recovered from having his bath?