This would be difficult to enforce either way, and even if we tried, it will be a losing battle. Some will
favor one, others will
favour the other, and us in between the two, fighting over a
u. The site's language is English, but I didn't see it specified anywhere if that's American, or British English. Probably for the better, as I personally wouldn't want to be forced in
favouring (or is it
favoring?) any side of the Pond, not in this day and age and on the Internet, at that.
And then there's a lot of users like me, trying to stick with one spelling, but occasionally and unwittingly mixing the two, either by force of habit, or typos that spell checker doesn't detect, because it's fine with either one of the two correct ones.
As for editing for grammar and spelling, try to follow the preference of the poster. If that's not clear by the poster's choice, use whichever you feel more comfortable in. We should avoid minor, insignificant edits as it is, not to needlessly move posts towards the community wiki status, with the limit of 10 revisions that keep the post authored. Edit for clarity, formatting, specificity, where necessary, and correct spelling and grammar while at it. See to it that any edit significantly improves user's contribution. Too hectic corrections might also discourage users to post more frequently, or even edit to improve their contributions on their own.
In short, one spells it as
color, the other one spells it as
colour, but they will both have to name the specific shade, if they care about any in particular. Insisting on either
colour will eventually (depending on their patience) only result in losing at least one of them, possibly both. And that's counterproductive.