It's a totally neutral blank canvas. Bring in whatever colors you want. I personally like a different color towel for each person using the bath. If you don't have shower doors find a shower curtain you like and pull colors from it for towels and accessories. Or find art you like and pull from it. Search houzz photos for ideas.

You could add some blue or green to the space. Here is a bathroom we designed for a client. All you need are some decor accents:

I’d paint the walls and choose a shower curtain and towels to complement...or choose the shower curtain and then find a paint that works with it. I wouldn’t let the neutral colors of the floor and vanities dictate your color scheme.

Biggest bang for your buck will be painting the walls a non-neutral color. Then select window treatment and shower curtain to go with that. Replacing the big single mirror with two framed mirrors will warm up the space dramatically, Use rugs that match your tile to make the space look as large as possible. A couple of colorful knickknacks on the vanity top will help as well. Put a floating shelf or two above the toilet and place color-coordinated folded towels to add warmth and color.

Another option is wallpaper. Many will like it - for me it is too much beige.