Purple Tang - what's this?

[jason604]

Was it in the middle of the night? I notice my fishes go really pale when I peak at night when they sleeping

[kien]

That's a neat trick! In 6 years I don't think I have ever seen my purple tang do that! I've seen him get less-purple when he's freaked out (fighting with a new fish, etc), but not WHITE. Wonder if it's a pigment mutation.