I do things above board — I'm not afraid of being investigated.
Tips
history
Used by 茅盾 (Mao Dun) in 《劫后拾遗》 and 周立波 in 《暴风骤雨》, where characters insist their conduct is 一清二白 — entirely above suspicion. Modern usage carries the same defensive flavor: declaring innocence rather than describing it neutrally.
memory
Picture two clean elements: 一清 (one clear) + 二白 (two white). 'One pure, two spotless' — doubly innocent.