This wiki is used in both America and The Commonwealth of Nations. This would be titled "American and British English spelling differences", but that could offend Australians, New Zealanders and other people in the Commonwealth who are not in Britain.
On TV Tropes, here's the guidelines (Please note that this applies to things like punctuation as well):
- Use whichever one you're comfortable with.
- First come, first served. Don't change the spelling in someone else's writing; this will just lead to edit warring.
- If there are strong national ties to the page in question, it's okay to standardi(s/z)e to one spelling. For instance, it's okay to change "colour" to "color" on Eagleland, and it's okay to change "program" to "programme" on British Brevity. The same goes for work pages; however, do not pothole trope names in the trope list — those should be left unaltered.
- Create redirects for titles with multiple accepted spellings. This makes the page searchable for both styles. Mixing styles in a title doesn't usually make much sense, though.
For comparison, here's the policy towards this on The Other Wiki.