> They are not generally considered indigenous. What about them?

I think there are examples, but it depends on how broad your definition of “colonized” is. The most extreme cases are the various isolated tribes of the world (of course, everything is interconnected, so a disingenuous person could argue that our impacts to the climate which affect their lifestyles constitute a kind of colonization, which is to say that disingenuous people like to stretch semantics).

> Examples of such groups

Virtually any non-indigenous people who have been conquered by an empire. The Irish are one of thousands of concrete examples.