If it is a British subject, use British English. If it is an American subject, use American English. If the subject is not specific to some English-speaking jurisdiction, use what ever version of English the article was first written in. Colour redirects to color, but accounting redirects to accountancy. Check out the Wikipedia policy page: "Wikipedia:Manual of Style (spelling)".
When I first started Wikinfo, I thought I would do it in American English, but as soon as a good editor showed up from England, that went out the window.
Wikipedia:Manual of Style (spelling)
Experience editing Wikipedia