Most small bodies fall in two camps: neutral (grey) or “red.” This runs through the Main Belt, even the Kuiper Belt past Neptune, and among comets. Granted, red isn’t like a stop sign, more of a tint in grey. Still, the division’s there. There aren’t green or blue asteroids… except the rare B-types. Large asteroid 88 Thisbe is B, and a crucial puzzle piece.
Most asteroids are C- or S-type, the above greys and reds respectively. Lesser classes like E- and D- fit the division too, for various reasons. In the S-types, iron content, especially when weathered by space exposure, adds a faint redness. C-type is named for measurable carbon contents; this overwhelms iron with an absorbent but neutral color. The C-bodies are thought to be more primitive, formed in cooler temperatures than S-. Carbonaceous meteorites, thought to be C-fragments, have mineral levels like the Sun, and are thought to represent the levels present as our Solar System formed from a cloud- the “presolar nebula.”
When the types were first offered in the late ’70s, C- and S- were obvious, but there were misfit bodies. Various planetary scientists claimed lesser classes, or simply U- (unknown) or X-type. Meanwhile, meteoriticists were subdividing the carbonaceous meteorites. As typing grew firmer in the early- to mid-’80s, it grew clear that C- and S- were groups or supertypes, needing subdividing too. The “C group” or “C complex” covers classical C-bodies, and the lesser B-, F-, and G-types, also thought to be carbonaceous, but varying somehow.
Studying any of the C complex informs us of the other types, by comparison, and counterexample too. This is “comparative planetology”- no part of the Solar System is boring if you want to solve the jigsaw puzzle. Since C bodies inform us of carbonaceous meteorites and the Solar System’s birth, fitting in bodies like 88 Thisbe tells us where we came from, and how we got here. Since carbonaceous bodies are also wet, they’re where we can go.