Ageto says hi.
There's conflicting information about that. I heard a while ago that it was possible to get a Shiny one, but then someone said that it wasn't possible after all. This has been going on for a while now, and I think it's best to just assume that all Shiny Celebi are hacked. Unless someone brings up concrete proof that they exist, I won't believe that Celebi can be Shiny.