"Darkness Visible"

"The sky was absolute and endless black, though in some fashion we could see stars and ugly cindered planets, visibly moving in chaotic paths; they were pieces of still deeper darkness, not an absence but a negation of light."
-Poul Anderson, Operation Chaos (New York, 1995), Chapter XXXII, p. 252)

"The sky remained black, with its more-than-black crawling orbs." (p. 258)

"A Dungeon horrible, on all sides round
"As one great Furnace flam'd, yet from those flames
"No light, but rather darkness visible..."
-John Milton, Paradise Lost, Book I, lines  61-63.

"For those rebellious, here their Prison ordain'd
"In utter darkness, and thir portion set
"As far removed from God and light of Heav'n
"As from the Center thrice to th'utmost Pole.
"O how unlike the place from whence they fell!" (p. 71-75)

Anderson and Milton address the same problem. Hell must be dark without any light yet those who go there must be able to see it. Hence, "...darkness visible..." etc.