Supermodel Bella Hadid, or as you know her, "one of those Hadids," has pretty consistently kept her hair a striking dark chestnut shade, even though she's naturally a blonde. That, however, may have changed, depending on whether or not Hadid is wearing a blonde-and-pink wig in this picture:
Evidence against: Hadid posted the below photo a few hours after she posted her pink haired photo. However, it's not clear that the woman in this photo is Hadid, or that it was taken after the photo she posted previously.
Plus, her hair looks light in this picture:
Hadid has said that she kept her hair darker so people wouldn't confuse her for her older sister Gigi Hadid. They certainly look alike even without the twin hair colors.