goldfish do
If you put a fish in a dark place the colour of the fish would gradually turn white.
No, once hair turns white, it cannot naturally turn dark again.
the lack of light being in the dark
Yes!
Fish turn silver, first around the gills and later throughout their entire body, as a result of bleaching due to ammonia poisoning.
It will eventually turn white.
It has been reported that goldfish will loose colour if kept in low light conditions so I guess if you are silly enough to want to not see your fish and keep them (it) in the dark to find out if it goes white that is your right.
-You can test if fish really do have just a 3 second memory(try training them, a T.V show 'mythbusters' tried it once) -Apparently, I heard that if you put a gold fish in the dark for long enough it will turn white.
Because it's dead
Fish tanks can turn white for a variety of reasons. Many fish shops can test the water if a sample is brought in. Typically white water is due to not being circulated or over feeding.
Usually dull coloured fish such as white and cream or dark coloured, such as grey and black.
Many things: moss, animal and fish waste, and pollution.