Ceres is a dwarf planet in the main asteroid belt, comprising about one third the mass of the whole belt and being the sixth largest body in the inner solar system by mass and volume. It has a round planet-like shape and a surface gravitational acceleration about 2.8% that of Earth. Observations indicate that it contains large amounts of water ice, about 1/10 of the total water in Earth's oceans. Since humans on Earth today only use a tiny fraction of the amount of water in Earth's oceans (even when counting freshwater and defining "ocean water" as simply the opposite of H2O in the mantle), that would clearly be enough for a major colony. The solar flux of 150 W/m2 in aphelion, which is nine times smaller than that on Earth, is still high enough for solar power facilities (average solar flux is 180 W/m2, or 13% Earth's). The Juno mission to Jupiter, for example, will be relying on solar power in a location further out from the sun than Ceres.
Being the largest body in the asteroid belt, Ceres could become the main base and transport hub for future asteroid mining infrastructure, allowing mineral resources to be transported further to Mars, the Moon and Earth.
Its colonization also could become a step on the way to the colonization of the objects in the outer solar system, such as satellites of Jupiter. Because of its small escape velocity combined with large amounts of water ice, it also could serve as a source of water, fuel and oxygen supply for ships going through and beyond the main belt. There is also a chance that this dwarf planet may have salt deposits.
The establishment of a permanent colony on Ceres might be preceded by colonization of the Moon or Mars. As a consequence of Mars' greater semi-major axis Ceres has more frequent launch windows to/from cislunar space than to/from Mars, and the travel time is lower. It is more energy-efficient to transport resources from the Moon or Mars to Ceres, than from Earth. In fact, transportation from Mars or the Moon to Ceres is more energy-efficient than even transportation from Earth to the Moon.
Ceres can have a subsurface freshwater ocean. It is possible that native alien life can exist. However, it could be a challenge for colonists because these forms of life could be anything from harmless microbes to strange, and potentially deadly sea monsters. If we colonized an earth like planet, or an icy world with subsurface oceans, one challenge we might have to face is the native, extraterrestrial life forms that could exist on those worlds. If they are deadly to humans, we would have to avoid them.