There will never be a true colony on Mars or the Moon. Why? Gravity.

The problem isn't the ability of adult humans to live and work in lower-gravity environments (despite all the problems identified in long-term exposure to microgravity). The problem is what happens to the development of the human fetus in the second and third trimester: the strength of the bones, the ability of bodily fluids to flow without the assistance of the 1G gravity we've evolved to use, and so forth.

The only ways we'll ever have true off-world colonization are (1) spin-gravity space stations that provide the gravity our bodies require, or (2) planets that are at or near normal Earth gravity e.g. floating cities above the clouds of Venus.

All other options sound nice for science fiction, but fiction is all they will ever be.