What's so special about grey?

Or gray? Why does it get to be spelled two different ways and pronounced and defined exactly the same? This seems to call into question all spellings and pronunciations in the dictionary. maybe there are other words like this that have a secret second spelling that they're (their? there?) just not telling us about. It's hard to stay focused on work when I'm focussed on this instead. And yes, both of those spellings are correct.