Hmm, do you have a picture?
Sounds like your palette is wide open for any splash of bright color.
You could head to walmart or target and have a look at the towels. Find a color you love and by a wash cloth. Take that to your local paint store or home improvement store and ask them to match it. If you love it on the towels you'll love it on the wall and then you'll know you'll be sure to be able to match with some accessories!
Personally I love a dash of red or Yellow in these type of settings. Your tastes may vary...but you can also take clues from other rooms for a more unifying approach.
Yellow would look awesome (if you like yellow!). Try bringing in some test color... hold up a pillow or piece of art in a color you are wondering about. Maybe leave it in the bathroom for a couple of days & see how you like it.
Also need to consider the light that comes in a window, if any.
I love to see black/white with spruce green color!
Thank you everyone! Went with a beautiful Black & white photo of rocks piled up along a shoreline, where a lone yellow flower pokes through....it is really striking....
Kathleen, I think we're going to need a picture :)
When I think of black and white floors I think of red stools at a 50's dinner. I think a pop of red would be great with your bathroom.