I have an idea that this a quote from either a poem or a book, but so far haven't been able to locate the reference.
The refrain of "Blackbird" by Paul McCartney is "Blackbird fly, Blackbird fly, Into the light of the dark black night." A slightly different sentence, "It was a dark and stormy night", is the opening line of the novel "A Wrinkle in Time" by Madeleine L'Engle.
Yes. I wondered if it was from "Under Milk Wood", but there the night is described as bible-black - far more expressive!