Natasha is blonde and Steve has a beard, which is presumably, because they are on the run since the events of Captain America Civil War (although Natasha was on the other side, and should not need to be on the run). But the way their first appearances in the film are shot, you are supposed to recognize them at first glance. The directors are basically assuming that their disguises are not very good disguises. And Falcon looks the same as I remember, so he isn't bothering with a disguise. Remember when Natasha used a mask that had to have been acquired on very short notice, to pass as a very high-ranking member of an international security apparatus? Just saying, maybe THAT's how you run around in disguise.

Also, I continue to love the ways Wakandans are so politically incorrect, but it's okay because they're black and explicitly anti-colonialist. Their name for Bucky is The White Wolf. There is absolutely no reason to call him White, there is nothing white about him, except his skin. He dresses exclusively in dark clothes and has a swarthy complexion and a grim brooding demeanor. It's just them being a little bit racist, in a way that's funny and doesn't hurt anyone.

I remain convinced that whoever is responsible for writing Groot in this and Guardians 2 has nephews. Baby Groot behaved exactly like mine did as toddlers, and now he acts exactly like they do in junior high.