The question to ask is not whether Mercury has the resources we need, but what we can do with the resources Mercury has.
Given a large enough initial colonization payload, in theory, any colony could continue almost indefinitely without additional input of matter. If we perfect the technology, we could colonize the space between Earth and Venus. Take this planet for example: We started with a, uh, REALLY big colonization payload, and we just keep going using the same matter, mostly. If we manage to destroy ourselves with some disaster like global warming, that will be a matter of management, not lack of resources.
To sustain a colony at or below its initial population, the only resource that is absolutely required is energy, which Mercurial colonists would get from the sun just like we do, in much greater abundance, if they can harvest it. If we want the colony to be able to grow beyond its initial size, it will need the materials of bio-matter, like hydrogen, carbon, oxygen, and nitrogen. As far as I can tell, we don't have enough information to assess those resources on Mercury yet. For example, although there is no significant atmospheric oxygen, we will probably find metal oxides in sufficient quantity on the surface. If not, the colony can only grow at the rate that we can throw comets at it. In any case, the main challenge is not lack of resources at all, but of technology.
Given only technology that already exists today, I don't think those colonists would have a snowball's chance on the day-time surface of Mercury of surviving the first Mercurial year. But once we have probed Mercury enough to have a strong sense of the variety of materials available, which will take decades or longer at our current rate, we need to determine if we can use those materials to build atmospheric containment structures, light reflection, dispersion and filtration materials, atmospheric replacement, soils, etc.
If we remain stuck on the idea that we need plastic or glass domes to contain our atmosphere and let in light, then a lack of silicon and petroleum will present a serious problem, but if we find a way to make a strong translucent material out of mostly hydrogen, sulfur, and magnesium, which we already know to be plentiful on Mercury, or out of something else we happen to find with our probes in sufficient quantity, then we're in business. We have barely scraped the surface of what is possible in materials sciences. We have only explored a handful of options that we have found to be interesting and useful for the challenges we face on Earth.
Edit in response to paul23:
I am not a materials scientist or chemist, but just off the cuff, I can see that water (H2O) is transparent as a gas, liquid or crystalline solid. Sulfur has the same outer shell as Oxygen, so what about H2S? There is plenty of Hydrogen and Sulfur on the surface of Mercury. So I decided to Google the properties of that chemical. It is most familiar to us on Earth as something that smells like rotten eggs, and readily dissolves in water to form a powerful acid. But I eventually found some interesting data here about it's chemical properties when isolated. In the absence of water, it is pH neutral and is transparent as a gas and a liquid. I can't immediately find any information about its opacity as a crystalline solid, but I know it can form a crystalline structure because it is a relatively high-temperature superconductor, which if anything makes it a lot more interesting as a potential resource for a Mercurial colony. Of course, the fact that it is a gas at low pressure and human-livable temperatures is an immediate engineering challenge. But look, I'm a layman giving it a few minutes of creative thought and doing a quick search on the internet. My goal is only to point out that you do not know what kinds of material properties researchers may discover until you look, and I suspect that we haven't even spent our first million on Mercurial materials science yet.
In any case, I'm certainly not buying the idea that sulfur just "won't be capable of creating" the right kind of crystal roster. We haven't done the science to find out yet! Some things, perhaps this thing even, may not have an easy solution. But other things may have extraordinarily awesome solutions. I mean, maybe a Mercurial colony would have to live deep under ground where they use their H2S superconductive technology to operate at high enough efficiency to reduce the burden of harvesting solar energy at the surface. There is a lot of research to do before we know what the pivotal challenges will be. I don't think it's time yet to throw up our hands and say those materials cannot possibly work.