No matter how they whitewash it, the scandal cannot be covered up.
Tips
history
Recorded in Ling Mengchu's Ming-dynasty 《二刻拍案惊奇》: 其涂脂抹粉,惯卖风情 — describing a woman skilled at making herself attractive. The figurative 'whitewash' meaning grew from there.
usage
The figurative meaning is far more common today and almost always negative — used for political or corporate cover-ups (为...涂脂抹粉 = 'to whitewash X').