As some people presume that Kali is the fierce aspect of Durga and Krishna is the god of love, there are adequate similarities between Kali and Krishna. These similarities are based on their forms and concepts. Here is a list of similarities between them.
The Dark Complexion : Both Kali and Krishna are either black or blue. The complexion represents the aura of the deity. The blue aura of Kali and Krishna represents divinity where as the black represents the darkness that consumes all evils.
Name : Both their names share a common meaning “the black one”. That is why Krishna is called Shyam and Kali is called Syama. Moreover in Bengal Krishna is called Jagannath and Kali is called Jaganmayee.
Nature and Cosmos : In Mahabharata Bala Krishna shows the whole cosmos inside his mouth to her mother Yashoda. In Hinduism it is believed that He is the holder of cosmos and Kali dances on cosmos so that every thing keeps going and the cycle of birth and death rotates. There is a deep connection between nature and cosmos to Krishna and Kali. Krishna is believed to be the holder of nature and cosmos and Kali is the cycle of birth and death of every being residing in it.
The Avatar philosophy : Krishna is the avatar of Vishnu and Kali is the avatar of Devi Mahatmayam. They descend for a common purpose to slay evil and restore truth and peace. Krishna is the slayer of Kamsa and Kali is the slayer of demons Chanda, Munda and Raktabija.
Association with battle field : Both of them are highly associated with battle fields. In Mahabharata Krishna is associated with the Battle of Kurukshetra and according to Devi Mahatmaya (Sri Sri Chandi) Kali is associated with the battle against Sumbha and Nisumbha.
Approachable forms : Krishna is the most approachable form of Vishnu and Kali is the most approachable form of the Mother Goddess. In India in most of the houses and workspaces (especially in hospitals) one will found the image of Kali or Krishna or both.
The Jagannath Idol : Jagannath of puri is considered the image of both Krishna and Dakshina Kali, Balabhadra as ‘Jyotirmayeem Tara’ and Devi Subhadra as ‘Adyasakti Bhubaneswari’. ‘Kalika Purana’ describes the four important Saktipitha and Orissa is one of them. The Dakshina Kali Temple of Puri has important religious associations with Jagannath Temple and it is believed that Daksinakali is the guardian of the kitchen of the Lord Jagannath Temple.
Deities with no mount : Krishna is seen with a Peacock and Kali with a Jackal. Other Hindu deities ride on their mount but Kali and Krishna never ride on them. Though Peacock and Jackal are symbolic but it also mean both of these deities work with the other beings of nature and each of every being has their own purpose.