Etymology: A pictograph of a long, pointed fingernail (popular in ancient China and also with contemporary guitar players). Phonetically used to express white.
Another theory is a pictograph of an acorn, which is white on the inside.
Hint: Use sun + stroke.
Mnemonic: SUNSTROKE LEAVES YOU WHITE (!?)
白書 (hakusho) white paper
面白い (omoshiroi) interesting
白人 (hakujin) Caucasian
(Based upon Henshall, 1998)