I hope you mean in 2072 and not in 2050 because Elon Musk promised to be on Mars by 2018.

Try colonizing Antarctica first, on the dirt underneath the ice. If that turns out fantastically popular, do the sea floor. If that succeeds beyond reasonable expectation, you can try out life in an orbiting donut. If that takes off, a Mars colony might have a chance.

SpaceX cans are woefully inadequate even to maintain a Mars outpost.

Ignoring the fact that multiple colonies already exist on Antarctica and living there is legally restricted to anyone without an army behind them, or that many people live under the ocean for large periods of time?

There are exactly zero colonies on Antarctica. Literally all are 100% dependent on regular deliveries of all supplies, excepting air and maybe water, from overseas, with no plan for that ever to change, and no permanent residents.

The usual term is "outpost", or for a larger operation, "base".

There are no undersea outposts, even. Construction crews sometimes encamp for a few weeks for big hazard pay. There are two (count 'em!) low-orbital outposts that get literally all supplies except energy from the ground.

The ISS is completely self-sufficient for water and air. No country on Earth is fully self-sufficient in what it uses and is dependent on supplies shipped to it from elsewhere.

The word colony in the sense of space exploration and other extreme habitats means permanent occupation and exploitation of the resources there.

Doesn't ISS generate oxygen from water and water is essentially shipped in? Either as water or as food. In the end methane is vented to space. I wouldn't call system needing pretty major inputs a self-sufficient one.

You are correct:

>4. Sabatier reactor

>Inside this machine, a blast of roughly 750°F heat breaks the bonds inside CO₂, forcing it into its constituent elements. The carbon and oxygen combine with hydrogen from the station’s ­oxygen ­generating system to make H₂O and methane (CH₄), the latter of which vents into space.

https://www.popsci.com/how-iss-recycles-air-and-water/

Every last molecule used on ISS is boosted from Earth, and recently. ISS does a bit of recycling to reduce the amount needed. There are exactly zero permanent inhabitants: any would die. They exploit no in-situ resource, except sunshine using frequently-replaced solar panels.