The Dark Goddess is a pretty big subject. Dark is not synonymous with discord, but with unseen. Dark/unseen includes the underworld and all un-seen, non-corporeal beings, and the natural death and rebirth cycles, also plants - think of all the seeds, roots and support system underground, caves, astral/ethereal experiences, unconscious soul-urges, earth critters that transform like caterpillars/butterflies, tadpoles/frogs, any being that is part one thing and part another or that can shape shift, the Fetch. The dark goddess would be associated with all of these. Primordial is a word often used, referring to a self-sustaining genesis of life force from the void.
White is a color of death surprisingly. Dead bones are sort of a dirty white color - Can't be too particular. A Burial shroud sheet is unbleached cloth, & the White Lady, White Goddess is a visitor from the underworld. So the Dark Mother can be white or black, black being absent light to see by, and thus being unseen, and of the night.
Do some research. And if you have any concerns on what you read, folks will contribute.