Belize is NOT a British colony. It once was, but not anymore. It gained independence in 1981. It is as much its own country just like the Australia, Canada, Trinidad & Tobago and many other ex-colonies. You may be confusing Belize with the Caymans, which are still a British Overseas Territory (along with Bermuda, the British Virgin Islands, Montserrat, Turks and Caicos, and Anguilla in the Caribbean).

Belize is still a constitutional monarchy though, identical to the United Kingdom, New Zealand, Canada and Australia, and QE II is still the monarch.