The name Kali means Kala or force of time. When there were neither the creation, nor the sun, the moon, the planets, and the earth, there was only darkness and everything was created from the darkness. The Dark appearance of Kali represents the darkness from which everything was born. Her complexion is deep blue, like the sky and ocean water as blue.
As she is also the goddess of Preservation, Kali is worshiped as mother to preserve the nature. Kali is standing calm on Shiva, her appearance represents the preservation of mother nature. Her free, long and black hair represents nature’s freedom from civilization. Under the third eye of kali, the signs of both sun, moon and fire are visible which represent the driving forces of nature.
Kali is not always thought of as a Dark Goddess. Despite Kali’s origins in battle, She evolved to a full-fledged symbol of Mother Nature in Her creative, nurturing and devouring aspects. She is referred to as a great and loving primordial Mother Goddess in the Hindu tantric tradition. In this aspect, as Mother Goddess, She is referred to as Kali Ma, meaning Kali Mother, and millions of Hindus revere Her as such.
Source: Kali – Wikipedia