The times when she appears in her “human” form are when she returns to the Mansion and when she’s spending time with Charles. We know that there’s contention between the two because of Charles risking the team while he gets to sit safely at home. She’s not okay with this and wants to leave with Beast, though she really cares about the younger team members, too. I guess her being in human form while at the mansion is a subtle protest to Charles’ risk-taking and arrogance. She can’t be herself around him, but she can when she’s away from him and with the team. And she does appear blue with him in the neighborhood scene, but you could assume that’s because what’s going on with Jean takes precedence over the beef Raven and Charles have. It’s not a super strong explanation - especially if it’s never directly referenced - but it’s better than having no reason at all. The fact that she was just arbitrarily human-looking in some scenes (especially while at her home) was irritating me. It does seem kind of similar to her reasoning in Apocalypse and, even though I wasn’t a fan of that, it makes it kind of work. I still would’ve preferred her be blue for the overwhelming majority of her scenes, though.