Since Black Widow joined Steve Rogers after he went into hiding, Natasha Romanoff had opted to dye her hair blonde in order to keep her identity a secret. As it turns out, she could have kept her red hair for the film. Concept artist Andy Park shares his work:
As you can see, they kept the green vest from this look, but I think it would have made Widow look a lot more different if they kept the scarf. Throughout her entire tenure in the MCU, I think Widow is the one who has had the least noticeable costume changes. At best, the only thing that changes with her look in the films is her hair. The rest of her image is just the signature black tights with the Widow logo on her belt and the weaponized cuffs.
Though I like the nod to the comics with Widow going blonde in Infinity War, I thought Marvel should have just kept her eyebrows dark. In some angles, the eyebrows actually disappear into her skin, and it looks kind of awkward. At least for the fourth film, it's been confirmed that Widow will go back to her usual red hair.
There had been strong rumors going around that the trailer for Avengers 4 would be dropping this November, but with the month about to end, it looks like the MCU is holding out till the last month. Friday the 30th looks like a good time to drop the trailer, but so far, we haven't been getting any kind of confirmation from an official source.
Catch Avengers 4 in theaters May 3, 2019.