There are major challenges to colonizing Mercury. For on it is difficult to reach. The environment there is not people-friendly. Radiation is a particular concern. Mercury does not enjoy the 'Earthlike' image of Mars and therefore had relatively little attention by comparison, but we still have a lot to learn about the planet.
Does Mercury have the necessary resources to sustain a human colony? Given that deep craters on Mercury's polar regions could provide protection from the searing heat and radiation of the closer Sun, a colony on Mercury could be possible. For any colony to be sustainable, it would need to be as self sufficient as possible.
So, would there be enough natural resources on Mercury itself to sustain the needs of a human colony?
Well, one large issue is that on Mercury we can't make plastics. Petrochemicals are needed as a raw material, and as far as I can tell, there were no dinosaurs on Mercury.
Bioplastics exist, but we would need a large plantation to be able to sustainably make plastics. We already would need large plantations for food and for sustaining the atmosphere, so this might get infeasible due to space considerations. Also, we need to consider the recycling of organic matter. Plastics are a dead end in the organic matter chain, they cannot be easily degraded to manure even if they are created from organic matter. On a planet where the building blocks must be shipped from the Earth, this can be a problem.
So, no plastic.
Mercury seems to have tons of iron though. That's good.