The etymology of 白 has multiple competing theories — most likely it pictured a grain of rice or an acorn kernel (a small, white, glowing thing) — but candidates also include a thumbnail or the white light of the rising sun. All theories agree on the visual: something tiny, white, and luminescent. Identical across 繁體 / 新字体 / 简体.

The character generalizes from physical white to abstract clarity / openness / declaration: 明白 (míngbai, "clear" / "to understand"), 告白 (gàobái / kokuhaku, confession — especially romantic confession), 空白 (kòngbái / kūhaku, blank space). The "blank / open" sense is one of the most productive metaphors in modern usage.

Mandarin: bái, rising 2nd tone. 白色 (báisè, white), 白天 (báitiān, daytime — "white time"), 白人 (báirén, Caucasian person), 明白 (míngbai, to understand — neutral final tone in this compound), 告白 (gàobái, confession), 蛋白 (dànbái, egg white / protein), 白菜 (báicài, bok choy / Chinese cabbage). Also a major surname.

Japanese: TWO on-readings — ハク (haku) and ビャク (byaku). ハク dominates: 白衣 (hakui, white coat / lab coat), 白人 (hakujin, Caucasian), 空白 (kūhaku, blank), 告白 (kokuhaku, confession — especially the romantic "kokuhaku" act famous in anime/manga). ビャク appears in older Buddhist compounds: 白夜 (byakuya, white nights / midnight sun — also read as hakuya). Kun-reading しろ.い (shiro.i) is the everyday adjective — 白い (shiroi, white). Also しろ (shiro, white as a noun) — 白旗 (shirohata, white flag).

The Japanese tradition of 告白 (kokuhaku) — formally declaring romantic feelings to someone — is a cultural keystone in dating, dramatized endlessly in anime and J-drama. The kanji literally means "tell-white" — to lay one's heart out openly.

Memory aid: a small grain of rice viewed against shadow — its inner whiteness defining the color.