Forbes says that Brie Larson does indeed look bored in the new trailer.
The colorful costume is in contrast with her deeply unimpressed facial expression
But Forbes says it's intentional because her character isn’t a young, zippy teenager, she's a jaded intergalactic warrior, an amnesiac one
What we’ve seen so far indicates that this is a story about a superhuman becoming human, rather than the other way around. And a superhuman as ridiculously overpowered as Captain Marvel is bound to be bored by the scale of her own abilities
Larson is playing an emotionally detached character
So yeah, she looks bored, but that's the point.