This is the 581st most frequent Japanese word.
黒
"Black."
The word "黒" is used as an adjective modifying "猫", indicating the color of the cat.
黒猫が庭にいます。
A black cat is in the garden.
The word "黒" is transformed into "黒い" to use it as an i-adjective describing "服" (clothes).
彼は黒い服を着ています。
He is wearing black clothes.
The word "黒" is used as a noun in this sentence to express the color black as the state of the night sky.