• 黒くろい — black (adj.)
• 黒板こくばん — blackboard
• 黒字くろじ — surplus
• 暗黒あんこく — darkness
• 黒幕くろまく — mastermind / wire-puller
• 黒潮くろしお — Kuroshio Current

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).

黒くろい 靴くつを 履はいています。
I am wearing black shoes.

黒板こくばんに 字じを 書かいてください。
Please write on the blackboard.