• 黒くろ — black (noun)
• 黒くろい — black (adj.)
• 黒板こくばん — blackboard
• 白黒しろくろ — black and white
• 黒字くろじ — surplus / in the black
• 真っ黒まっくろ — pitch black

More examples ▼

• 暗黒あんこく — darkness
• 黒幕くろまく — mastermind / wire-puller
• 黒潮くろしお — Kuroshio Current
• 黒人こくじん — Black person
• 黒豆くろまめ — black soybeans
• 黒猫くろねこ — black cat
• 白鳥黒鳥はくちょうこくちょう — swan and black swan
• 黒星くろぼし — black star / defeat / loss

This character originally showed a fire burning under a cover, producing soot — symbolizing darkness and blackness. Over time, it also gained the nuance of "bad" or "wrong" in contrast with "white" (good/pure).