It's used to refer to black fur, and also has mourning connotations.

You'll frequently see the poetical allusions to mourning using the word "sable", e.g.,

"Yet Fancy and Invention never die; they watch with keen and scrutinizing eye how to give diversity even to the sable hue of solemn black, and to mingle variety even with the solemn drapery of mourning."

(December, 1817, La Belle Assemblee, after the death of Princess Charlotte.)

Respectfully,

Louisa