If you would accept darkness as referring to night, then you could use "His eyes were as black as the dark of night."
The joker from dark knight
"Like a blind person in a dark room."
he/she has a heart as dark as the deepest depths of the ocean
This simile is comparing the dark Caribbean ocean with moist(ocean) black (dark night) cake.
yes.
he/she has a heart as dark as the deepest depths of the ocean
Its a personification
As dark as a racists sole
Her mood was like a dark storm cloud looming on the horizon.
Personification. A simile would compare two things, such as, "The library was as dark as the inside of a coal mine at midnight," or "The library was as quiet as inside the losing team's bus heading home."
yes there is a simile for e.g snow white hair was as dark as the night sky
You are a hot candle.