Sci-fi book where almost everyone has same color hair?

Help me remember the title of a sci-fi book I read years ago (and I believe was on the shelves for a while at that point anyway) where most of the Earth’s population had IIRC brown hair, except for the protagonist, who had blonde (?) hair.

I remember her being described as wearing a cap or hat most of the time, to hide her difference, and I recall a passage where a lock of her (long) hair slips out from under its cap, and she hurriedly tucked it back in out of sight.

Ring any bells?

Are you thinking of Harry Turtledove’s “Darkness” series - a fantasy WWII, in which blondes are a distinct minority in many countries, and are persecuted by the brown-haired majority in those nations?