I would use Alabaster (wall paint color) on everything in the room (walls/ceilings/trim).

I would have done that sloped section in the wall color. There are no rules, some rooms look better one way and some the other way.

If you do the walls, sloped ceilings, and flat ceiling in the wall color then any awkward angles pretty much fade away and everything looks much more cohesive.

However, if you don’t want to paint the flat ceiling in alabaster, I would still do the sloped ceiling to match the walls.

I’d probably keep the sloped ceilings the same color as the walls if they’re low. Using SW Alabaster on both can make the transition feel more intentional and cohesive, while painting them ceiling white may visually emphasize the slope.

Why two colors at all? They are not a great combination--one is very white and the other more yellow-ish. Too close for contrast. I'd paint the entire room one or the other, whichever works better with the furnishings.

All one color and probably alabaster