Here I offer some idioms which contain the word “Black”.
1) as black as a skillet: very black
My hands were as black as a skillet when I finished working on the car engine.
2) as black as a stack of black cats:very black
The little boy was as black as a stack of black cats after playing outside all day.
3) as black as a sweep: very dirty/black (a chimney sweep cleans chimneys and becomes very black)
My friend was as black as a sweep after he finished cleaning the basement.
My friend’s cat is as black as coal.
5) as black as night: very dark and black
The old house was as black as night when we entered it.
6) as black as pitch: very black
My face was as black as pitch after cleaning the stove all morning.
7) as black as the ace of spades: very black
The horse in the parade was as black as the ace of spades.