Out of curiosity, is there any reason why you can't use a color that you've already used in the other bathrooms, especially if they're not very close to each other (e.g., on different floors)?
Also, is this bathroom linked to a bedroom? If yes, it might help to use a bathroom color that complements the bedroom color scheme.
Unless you've got a large, airy bathroom, I'd advise against dark colors (like navy blue or dark brown). From experience, it feels oppressive in a small bathroom, although with the correct lighting it can still work.
Having said all that, yellow might be an option since you don't appear to have used anything like it. You can use dark colored accents (paint borders, stripes, or dark-colored bathroom fixtures) to add contrast and make the bathroom more interesting.