Here is a picture...

you could do an accent wall in the bathroom like the picture below. I would use the revere pewter on the ceiling which ever direction you decide.

if you have four walls you can play with the design. You could also do revere pewter at the bottom of the wall with sea star on the top part of the wall and revere on the ceiling

How about a blue gray color like November Skies from Benjamin Moore? I like your floor color. Is it wood or tile?

I think a powder room is the perfect place for a darker, dramatic color. Benjamin Moore Hale Navy is a true navy. Be sure to use a high hiding primer over your red so you get a true color. A gray primer might be best.

if you really want navy blue I would use it as an accent wall. Navy blue is too dark and it definitely too dark for a small room Dark colors make a room appear smaller and gloomy.

I like the navy katinparadise posted, but I wouldn't go and darker. However, I would still use it as an accent color.

123 primer is very good as well