Magearna forms?

So I've been looking at all of the Pokemon here that have multiple forms on the Wiki and noticed that Magearna has a sprite for its grey colored form. The thing is, Magearna normally comes in its original red and gold color when it hatches. Is it possible to change Magearna to its grey color and how can I do it?

you have to have it for a long time in order for it to be the gray/ grey color and you can not change it back nor is it possible to hatch a gray/grey one

So after a long while it just turns into the grey Magearna?

I think this isn't true. I hatched my magearna in 2017 and it is still red. I believe the grey form only comes as easter egg as egg bringer? (Where it would normally be shiny for other legends) not 100% sure on that though

I don't think so. They are supposed to change colours over time, but Niet said that it would be a very long time. And I honestly don't believe the alternate colour forme is even coded into the game, excluding the Legendary Egg bringers.

I asked Shazi on discord how to obtain the grey colored one and she said it wasn't possible to get it

Maybe in a few hundred years, like the lore indicates.