Spelling...gah

I've just been reading through a comment that one of my beta's sent ( showing that one typo that *always* misses the net 'till you post) She mentioned some spellings that I'd left in Brit form rather than US. I usually don't change how I spell. My words have 's' instead of 'z' I write colour not color etc. I suppose my question is does that even matter?

I always change the words I use if I'm writing for an American show, closet=wardrobe trashcan=bin the list goes on, but I believe that you *have* to write how your characters think. Just the same as I would expect anyone writing QAF UK or Professionals to use Brit words.

But spellings as well, surely that's going too far?