We have been on both the three night and the four night
Disney cruise. There isn't a "theme" to the dinners, but the different restaurants created different moods. Triton's was the more formal one, and I'd say Parrot Cay was the more casual one, with Animator's Palate in between. The first time we cruised I think we all felt overdressed. I wore dinner - type dresses, DH wore a suit, DD17 wore dresses and DS11 wore dress pants and a shirt. While there were some people in dressy clothes, the majority were in a more casual look. I did see a woman wearing a formal gown near the elevators, so I at least felt less overdressed than her!
The second cruise we all took it down a notch. DH wore Docker type pants and a nice collared shirt, I wore a dress in Triton's, but I wore capri pants/top in the other two restaurants. DD still overdressed, but she likes too! DS13 wore his khakis and a polo.
I think the 7 night and longer cruises are the ones that have theme nights for dinner and a formal night as well.
Wear what you are comfortable in, but not beach wear type stuff.
Hope you have a great time!
