Though Black Widow's skills as a spy and superhero remain steadily consistent, she's never been shy about changing her hairstyle, be it in the comics or throughout her Marvel Cinematic Universe appearances. One movie would see her with long curly hair, the next with short hair, then the one after that, back to long, but straight. In a sense, her constantly changing look has managed to be a subtle reflection of the character's ability to shift from one role to the next, from spy to superhero and back again.
With the release of Vanity Fair's four Avengers: Infinity War covers, we see that Natasha Romanoff's new-film, new-hair tradition is still very much alive. This time, however, the change is more drastic than ever: Black Widow has changed her red hair to a striking blonde. This marks the first time that Widow's signature hair color has been altered, and it inevitably leads to the question: Why?
The most likely answer, one that makes sense for the storyline established in the movies, is that Natasha has gone back undercover. When S.H.I.E.L.D. fell after the Hydra takeover in Captain America The Winter Soldier, Natasha leaked all of the spy agency's intel online, releasing information about her own past covers and secret identities as a result. Black Widow ended the movie by revealing that she had new cover identities to create.
But as we picked up with her in Avengers: Age of Ultron and Captain America: Civil War, Natasha wasn't living in hiding. She was a full-fledged member of the Avengers. That is, until the Sokovia Accords tore the team apart. Natasha may have sided with Team Iron Man, but when push came to shove, she stood alongside Steve Rogers, turning on Black Panther in order to allow Steve to make his escape. We later learn that T'Challa had told Secretary of State Thaddeus Ross what Natasha had done, indicating that the government would be coming after her next. The last we saw of Natasha, she was leaving for parts unknown -- after Tony Stark gave her a proper warning that the government would be coming for her next.
This means that going into Avengers: Infinity War, Natasha is most likely a hunted fugitive. What's more, she has none of her previous cover identities to fall back on. Natasha is smart, and she knows that the government will be looking for a redhead first and foremost. Changing her hair to blonde makes it much easier to go by unnoticed by government watchdogs. Leaked photos of the upcoming film have indicated that Natasha will find herself fighting alongside Captain America and Sam Wilson once again, seemingly confirming that while she may have a new identity, Natasha still can't help but fighting the good fight, even with the full might of the United States government after her.
It's also possible that the Widow's new hair color is a nod to the comic books. The second character to bear the Black Widow mantle was a blonde woman named Yelena Belova. Like Natasha, she was Russian, and had been trained in the Red Room to become a deadly spy and assassin. While it's unlikely that the character heself will appear in the film, perhaps the new cover identity Natasha created for herself is named after the second Black Widow. If you hear the name in the film, you'll be able to recognize the Easter egg.
As the Avengers band together once more against the might of Thanos, don't be surprised if, before the final battle starts, Natasha dyes her hair red once more. It's a part of who she is, after all, and it's as much a signature look as Captain America's shield or Tony Stark's armor.
Directed by Joe and Anthony Russo, Marvel’s Avengers: Infinity War stars Robert Downey Jr., Josh Brolin, Mark Ruffalo, Tom Hiddleston, Chris Evans, Chris Hemsworth, Jeremy Renner, Chris Pratt, Elizabeth Olsen, Sebastian Stan, Benedict Cumberbatch, Paul Bettany, Samuel L. Jackson, Cobie Smulders, Benedict Wong, Zoe Saldana, Karen Gillan, Vin Diesel, Dave Bautista, Pom Klementieff, Scarlett Johansson, Tom Holland and Anthony Mackie. The film opens May 4, 2018.