Where the shape comes from
The readings differ — a thumbnail, an acorn, a grain of rice — but the one that carries best is the sun 日 with a single ray rising from it: the first pale light of the day, and so the colour white. From white comes empty (白纸) and clear (明白, 说白了). Its section is small but heavily used: 百, 皇, and the 的 that ends more Chinese sentences than any other character.