As far as the Hadids go, there's been a pretty reliable hair color equilibrium maintained—Bella and Anwar with their dark brown hair, and Gigi and her mama Yolanda with their dirty blonde beach waves. There was that one time that Kendall and Gigi swapped hair at the Balmain show, and it basically broke the Internet, but that's the most we've seen Gigi experiment with hair color until now.
The last few days, Gigi has been out and about in New York sporting noticeably darker hair. You can classify it in the ombré/bronde hair genre.
If you want to get really investigative with it, we should mention Gigi has been slowly fading out her beach blonde hue for a couple of months now, but now it's more clear than ever.
We're not sure what inspired the new look, but we have a few guesses.
Gigi seems to be spending a considerable amount of time in New York and perhaps was inspired by the fall(ish?) weather?
She also might have been inspired by Zayn Malik's darker locks (#Zigi). Finally, maybe she was inspired by her siblings' darker hair. There's also the possibility that this is closer to her natural hair color and she's just stopped getting regular highlights. And if that's the case, girlfriend, we feel you. Keeping up with salon appointments is a lot.
Either way, she looks amazing and radiant.