You can do it either way. I can see why they did it this way, it makes it look like you have taller walls in the room.

I would refresh the ceiling with new white paint, including the angled part. Then pain the walls you new blue color. Now you can live with the room for a few days/weeks and decide if you also want to paint the sloped ceiling blue or even the whole ceiling blue.

Walls and ceiling should be all one color, IMO. It removes the top off the box.

This illustration shows how one color can minimize different angles.

Have you considered wallpaper and a runner for the entry? I think white is appears too ordinary, thinking you need color which works with the walls and the rug.

Sharing my go, love it, use it, teal…B.M. Sea Star. I used it in a client’s dining room and it, like yours, with good light. Beautiful.

(These colors in the Thibaut wallpaper are what I see of the rug on my monitor).

Do it all one color.

all one color