A Question About Space and Colonialism

This is something I've been thinking about lately, so I thought I'd pose this question:

Is space exploration or human migration to space colonialist?  To clarify, I'm asking here about real life, not in fiction.

If so, *why* is it colonialist?  If not, *why* is it *not*?  What writings or works have informed your thinking on this matter? 

I've been having a lot of thoughts and reading up on this question lately, and have been working on refining my own opinions about this, but perhaps other people have read or thought of something illuminating that I haven't.