The possessive of a single species: "Species's colouring", or "Species' colouring"?

[BelfastBloke]

Have I spelt that right? - am now in doubt.

"Species' colouring"

Or, if you're really not sure, "the colouring of the species"

I think either is technically fine, but I like "Species' colouring" better personally, because it's closer to how I'd pronounce it.

So you would also say Charles Dickens' Great Expectations? Not Charles Dickens's Great Expectations?

Why?

Yes, as in "Charles Dickens' Great Expectations is excessively sentimental pap."