"soft darkness" is a correct and usable phrase in written English.
It can be used to describe an ambient, peaceful atmosphere. For example, "The soft darkness of the night created a romantic ambience for their anniversary dinner."
In the wild soft summer darkness How many and many a night we two together Sat in the park and watched the Hudson Wearing her lights like golden spangles Glinting on black satin.
Even in this darkness, he saw wet gleams upon her eyeballs, like faraway fireflies, and the pallor of her long belly descending to a small soft shadow.
But the light was soft and the darkness was softer, and Carol Grey at that moment was beautiful.
On the rare occasions I do come across another nocturnal wanderer, we seemingly glide past one another, each in their own safe and soft cushion of darkness.
The Shakespearean bed trick, where it is so dark that somebody ends up making love to the wrong somebody (or as it happens, ultimately the right somebody), could never happen in our bright bedrooms, but the soft velvet of darkness turns even a familiar lover into an unknown encounter.
The concerto starts in flickering darkness, with soft, shuddering low strings interrupted by a solitary flute melody.
This is what the soft quiet cover of darkness is about.
Writer Charles Taylor states, "Betty and Rita are often framed against darkness so soft and velvety it's like a hovering nimbus, ready to swallow them if they awake from the film's dream.
Our dreams are what keep us going through the cruelty, darkness and soft bigotry of lowered expectations that is, unfortunately, all too much a part of our daily lives.
The soft performance of "Edge of Darkness," which took in only about $37 million in foreign theaters after its release in January, increased skepticism about his bankability.
