https://www.cnet.com/news/avengers-endgame-drops-surprise-trailer/

It kicks off a series of mostly black-and-white flashbacks to the various Avengers' past adventures and the vanishing caused by Thanos' snap in Avengers: Infinity War.

We see Hawkeye and Black Widow with a variety of haircuts in the color shots, hinting at either a fashion crisis or that we'll be hoping to different points in the timeline.