If you would accept darkness as referring to night, then you could use "His eyes were as black as the dark of night."
Your Mom and mine too
sharp as lead
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.
Its a personification
he/she has a heart as dark as the deepest depths of the ocean
yes.
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