Several parts combine into one character.

The etymology of 黑 has competing theories — either the soot-stained face of someone who has worked over a fire/chimney, or the marked face of a tattooed criminal. Both involve 灬 (the four-dot fire-foot radical from earlier batches) at the bottom and a face/body element above. Either way: dark stains on a face. Three forms: 繁體 黑 / 新字体 黒 / 简体 黑. Note the Japanese shinjitai 黒 simplified the four fire-dots (灬) at the bottom into 土 (earth) — the only major split between Japanese and Chinese in this character.

The character anchors many color and metaphor compounds: 黑白 (black and white — both photography and "right and wrong"), 黑暗 (darkness), 黑色 (black color), 黑板 (blackboard), and figuratively 黑人 (black person), 黑市 (black market), 黑帮 (criminal gang).

Mandarin: hēi, level 1st tone. 黑 covers physical darkness and metaphorical "secret / illegal": 黑色 (hēisè, black), 黑板 (hēibǎn, blackboard), 黑暗 (hēi'àn, darkness), 黑客 (hēikè, hacker — phonetic loan from English "hack"), 黑社会 (hēishèhuì, criminal underworld). Note 黑 has acquired strong "illegal / underground" connotations in modern Mandarin slang.

Japanese: on-reading コク (koku) — 黒人 (kokujin, Black person), 黒板 (kokuban, blackboard), 黒色 (kokushoku, black color), 暗黒 (ankoku, total darkness), 漆黒 (shikkoku, jet-black — "lacquer-black"). Kun-reading くろ.い (kuro.i) is the everyday adjective — 黒い (kuroi, black). Also くろ (kuro, black as noun) and many surname uses: 黒田 (Kuroda, "black field").

The Japanese 黒字 (kuroji, "black letters") means a financial profit, paired with 赤字 (akaji, "red letters" = deficit) — same accounting metaphor as English "in the black / in the red".

Memory aid: a face stained by chimney soot — direct visual definition of "black".