If Black Widow does direct connect with the events of Infinity War, it could clear up a major physical change for the title character. Namely, her short blonde hair that she had when rocking the aforementioned green vest. Natasha Romanoff is known for her signature red locks, which have been styled a variety of ways during her tenure in the MCU. That’s why it was so surprising when she was blonde in Infinity War, especially as no reason or context was given. But perhaps that’s because it was going to happen in her solo movie all along.
Article source: https://www.cinemablend.com/news/2485921/the-black-widow-trailer-has-a-surprising-connection-to-avengers-infinity-war