Update. I played it, then played it again, and so on. Hooked.
Too much to write on the Civilization Games Wiki, where it doesn't quite fit. So it's now on a brand-new wiki, http://imperialism.wikia.com - where the many things that are not mentioned on the in-game Help screens can be covered by contributors with experience and/or access to a Manual.
It had a sequel, "Imperialism II: The Age of Discovery", which has more elements that will be familiar to players of "Colonization"; it seems to be also downloadable at no charge from a different website. It's mentioned on the wiki too.
Players of either game would be most welcome to join in and make the wiki a more useful resource.