Bai qie hei describes a character who looks mild, well-behaved and harmless but is calculating inside. The literal reading is 'white outside, black inside', and the label is used for heroines and heroes alike. The gap between the front and the real person is the pleasure of the type, because the audience knows the secret before the other characters do. Quite the Girl is built on it: the obedient 'good girl' persona is her cover.
Dramas
Where it comes up

Neon & Nine-to-Five
Quite the Girl: A Vertical Micro-Drama Hit Rebuilt as a Long-Form Revenge Romance
A guide to Tencent Video's Quite the Girl: a heroine who plays the obedient niece to use a wealthy heir against her uncle's family, how a hit vertical micro-drama was rebuilt as a landscape long-form series, and what its two leads, Xu Mengjie and Ren Shihao, bring to it.
