One of mine gets totally white he almost looks like a Cambodian. One day when I was changing his water, I ran out of conditioner and took the chance on leaving him on the table. By the time I got back half an hour later, his normally very red body was so white I thought he had died .... poor little fishy. But he was perking up when I placed him back in his tank and I watched him change colour from white to red within a few minutes. Then everything was good and I fed him some bloodworms to make him forgive me.
The container I left him in was much smaller than his 3.5g tank, no wonder the poor little guy was stressed ....