Why not a paler grey than the floor, keep it all monotone and don't get too dark. Use bathroom paint for some reflectivity and ease of cleaning.
Grey is easy to live with but you need to think about whether you want a cool or a warm grey.
Bring home your 4 favorites in sample jars and paint cardboard at least 2' x 2' and live with the samples for a while each in different places in the room at different times of the day to see the changes when the light hits.
Lots of possibilities for accents with a great grey....
Regards,
Karen & Joseph
for Decorative Philosophy

A small bsthroom can take everything in grey, including the vanity (perhaps in a gloss laquer) the iniform colour opens up the space... Just change it texturally, using river rock or some other interesting tile in the same colour