How high exactly are the ceilings? Pictures are tough, but it looks like maybe 12 feet? Depending on the exact height, I would paint the lower 2/3 (or at least the lower 8 feet) a light or medium color, any color you like. Then the upper walls and ceiling a much darker version of that color. No accent wall--that would really highlight the odd proportions of the room.

I would be tempted to put in a drop ceiling. I wouldnt want my bathroom ceiling that tall. All the fixtures look a bit short and out of place, with that high ceiling.

is the vanity countertop a different color than the fixtures?

I too would paint the upper portion a darker tone to bring it down to a comfortable height.

a blue, for me. is there a ceiling electrical box? if so add a dramatic hanging light fixture to fill the space. Since the tile and hard surfaces are white, I would choose a very soft blue, White with just a hint of blue, so not to clash with the other whites, and off whites.

Hi- the ceiling is like 18 ft at the top of the slant

Keep it one color for now.
Well talk later about the remodel.

18 feet--yikes! I would choose the proportions based on the height at the lowest point. Dark upper walls and ceiling will help the ceiling feel closer, and minimize the visibility of the slope. I would also add simple molding at the color change, painted the same lighter color as the lower walls.

The reason you're getting a lot of different advice is that there isn't just one right answer. Ask ten people you could get ten different opinions. It is a challenging space to work with. So for what it's worth, here's my two cents. I would paint the walls and ceiling a light to medium blue-green. The sink is beigey, but the tub and tile are white, so be sure to sample colors next to both before you get up on a ladder to do that high ceiling. If the remodeling is going to be done within a couple years, don't do anything. Save your effort. Right now it's uninspiring, but as long as everything works you should be able to let it go for a while. We have seen uglier bathrooms on posts here. :-)

It's all builder's grade. I would not bother to paint and just accessorize for now.

Curtains to the window, pretty towels, shelves over the toilet, glass jars with soaps in them on the tub, towel ring at the sink and add tall artwork over the tub on the shower side.

Build a lowered ceiling platform, and add a drop down attic stairs. No one wants or needs ceilings that high in a bathroom. But everyone needs more storage.

A skylight and tropical plants that like humidity might be nice. Well it's a thought!

Drop the ceiling! It's an absurd height for a bathroom : ) Remodel or no remodel. Nothing more than nine feet. then pick a wall color that links to your bedroom bedding or wall color . Add accessories, towels rug etc

In the mean time, I would consider doing something like painting the walls an actual color below a horizontal line 9 feet above the floor and everything above that the "ceiling" color.

Here are my inspiration pictures of bathrooms with high ceilings followed by a sketch of a spa looking one of yours (not exactly your layout but didn't have pictures of entire bathroom).

Hang curtains at ceiling height with a roman shade over the window but hung high above to make the window look taller. I show the ceiling in natural wood but it could also be painted either white like the walls or a dark colour to give the illusion the ceiling is lower.

If you’re going to remodel the whole room, I would just leave it unless the paint is so dirty you can’t stand it. I also have very high ceilings in my house, and in my small powder room (10 feet). I will be remodeling it using wainscoting with wallpaper above it AND on the ceiling to try to “bring it down”visually.

If you’re up for a weekend project, then try using one color below and a darker color above and see how that feels.

IMO lower the ceiling then do what ever style and decor you like