Darkness in a dream usually points to the unknown -- the unconscious part of a situation, or of yourself, that hasn't been illuminated yet. Moving through it without panic can reflect a growing willingness to face uncertainty, while fear of the dark often names a more specific worry about what you might discover if you looked closer.
The best artist in the world may chance to err, when he mistakes a true significator for a false one. - William Lilly (1602.-1681.)