Yes, that is exactly what I would do. That is the new trend in painting and in fact, if you paint one central wall a different color than the two other, the room will appear bigger as well. I would suggest that you paint your washroom a dark beige color. Dark beige goes well with a medium brown. Since it is a washroom, you want to keep it neutral. Paint one wall an even darker shade than the color you are going with. Other colors that may work well are a pale yellow.

Sky blue and beige work excellently with medium brown. If the tub is near a wall, have you considered tiles? Beige tiles to half the height of that wall with the rest of the area of the walls painted sky blue would look great.