Dusky, a.
1. Partially dark or obscure; not luminous; dusk; as, a dusky valley. Through dusky lane and wrangling mart. Keble.
2. Tending to blackness in color; partially black; dark-colored; not bright; as, a dusky brown. Bacon. When Jove in dusky clouds involves the sky. Dryden. The figure of that first ancestor invested by family tradition with a dim and dusky grandeur. Hawthorne.
3. Gloomy; sad; melancholy. This dusky scene of horror, this melancholy prospect. Bentley.
4. Intellectually clouded. Though dusky wits dare scorn astrology. Sir P. Sidney.
Shades of meaning
Fernald has no entry of its own for dusky; he lists it under dark, obscure.
Where he writes about it:
Dusky is applied to objects which appear as if viewed in fading light; the word is often used, as are swart and swarthy, of the human skin when quite dark, or even verging toward black. — from dark