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Yeah, I meant earthy as in the definition of earthy, I guess.

Resembling or suggestive of earth or soil: "an earthy smell"

Another note, not that you don't have plenty of help already!

A coticule should give off a definite earthy-musty odor as you lap into it (no, not like breast milk!). If it's synthetic it will...

That looks like a "vintage" coticule. If it is, then the likelihood that the dark side is Belgian Blue (and not slate) is fairly high.
It also appears that the dark side is dished in the middle...