Sorry to disagree, Katzmeow, but in fact Chi's policy is, in nearly every case, to give equal status to 'British' and 'American' spellings;
colour/color,
centre/center etc are all equally common.
If it were just a case of one being 'British' and one being 'American', then
modernise and
modernize would have the same classification.
However, you may be surprised to know that the policy of Oxford Dictionaries (regarded by many as the ultimate reference) is to give the '-ize' form as the 'primary' spelling and the '-ise' form as the alternative.
This is not an attempt on the part of the OED to be 'trendy' or 'American' but to closer reflect the spelling of the original Greek words that these English words derive from.
Oxford spelling is best known for its preference for the suffix -ize in words like organize and recognize, versus the -ise endings that are also commonly used in current British English usage. The spelling affects about 200 verbs and is favoured because -ize corresponds more closely to the Greek root, -izo (-ιζω), of most -ize verbs. In addition to the OUP's "Oxford"-branded dictionaries, other British dictionary publishers that list -ize suffixes first include Cassell, Collins and Longman.The whole Wikipedia article is here
https://en.wikipedia.org/wiki/Oxford_spelling