Dark vs. Light and Domination vs. Submission

Throughout the novel, words such as dark, demon, evil were used and occasionally the opposite of white and light. These references seemed to go along with the dominating and submissive theme. In the chapter Woman to Woman, Hermione was compared to a priestess and shortly following Ursula speaks of Birkin's demon part and his wanting for her to submit. Earlier in the novel, Birkin was seen as white/light especially when Gerald was observing him. The adjectives used to describe Hermione were usually dark before now. What is the significance of this reversal?  Was it always there, thus the reason why Birkin would not marry Hermione like she wanted. It almost seems like Birkin wants to dominate someone who doesn't want to submit which mirrors his relationship with Gerald. And then at the end of the chapter, the roles seem to return to their previous state. There is significance to the reversal I'm sure, but currently the meaning eludes me.