Official policy on regional spelling from the Archive is that an author is quite entitled to use their own regional spelling if they want to. The only thing we like to see is consistency.
If I was beta reading or GEing a story, I'd certainly point out that an author was using colour one minute and color the next and ask them to pick one or the other and run with it.
I think phrasing though is a different matter. Especially when it comes to dialogue. At a personal level, I always like to get the phrasing to match the characters and location of the show I'm writing for. So I would appreciate an American pointing out that LNC would never say 'fortnight', for example and try to remember not to use it again.
But, again, whether to go with that kind of accuracy or just use your own regional phrasing in the mouths of characters is pretty much an individual author choice. If I saw that kind of thing while editing I'd point it out, but if the author didn't care that would be up to them. I don't think the fandom has any fast and firm rules on that one. Certainly, the Archive doesn't.
LabRat
