Forum Moderators: open
[added later]
Just in case this is a question of British (Australian, Canadian, South African, etc.) spelling as opposed to the US, I should note that American spelling is used for category names in most of the directory. An exception is made for subject categories under the Regional [dmoz.org] hierarchy: in English-speaking countries where British spellings are used in print and online media, the local spelling is used for category names. This applies only where the population speaks English-- the Denmark category uses "Transportation" instead of "Transport" and Pakistan uses "Real Estate" instead of "Property" even though the British form is probably more familiar there (q.v. Regional Guidelines: Subject Categories Template [dmoz.org])
In descriptions, some leeway is granted to the editor. When I edit in a subject (non-Regional) taxonomy, I use the spelling and terminology local to the site-- a colourful art exhibit in New Zealand, a colorful one in Canada; a gaol conditions activist group in Scotland, a jail conditions activist group in the US. This is not an explicit rule, however, so it is not unheard of for an Irish editor to call all US cricket teams "organisations" or vice versa baseball fanclubs in Ireland "organizations."