Feng Shui is an artistic philosophy held by the Chinese, based on the combined energies of astronomy and geography. Before beginning a Feng Shui project for your home, you may wish to obtain a Bagua map, which often is used in Feng Shui to determine which rooms should have which elements associated with them, though this is probably more useful when you are decorating multiple rooms of your home.
When decorating your bathroom, color is always an important consideration. When you want to incorporate Feng Shui, however, it is perhaps doubly so. You are not just choosing a color that is pleasing to you, but one that represents one of the five Feng Shui elements, Wood, Metal, Fire, Water, and Earth. These elements each correspond to a different set of emotions and should be chosen accordingly. You probably would not want, for instance, a bathroom that inspires high energy as the Fire element would convey, nor one that represents nourishment as Earth would do.
When choosing for your bathroom, you should use combinations of Metal, Water, and Wood elements. The corresponding colors for these elements, in order, are grey and white, blue and black, and/or brown and green. The reasoning behind these color choices are relatively straight-forward. Metal stands for efficiency and lightness, as well as clarity, which should encourage a clean bathroom, as will water as it also stands for purity and freshness. Water colors also bring a calming effect to a space, making your bathroom a place where you can relax, such as in a warm bath. Since the bathroom is often a place where one heals wounds and keeps a medicine cabinet, the Wood element colors are essential, to promote good health.
Finally, the strength of these color choices will depend a great deal on which direction your bathroom lies. Metal is closely associated with West and North and will function better in rooms that are in those directions. Water is best in the North, East and Southeast, while wood is best for the South and East. You may find that placing these colors on the corresponding wall will be of great benefit, or simply sticking to the colors that best align with the compass direction of your bathroom. You may also want to incorporate art with the animal associated with the direction. And shades of these colors will do, though vibrant colors are certainly encouraged by Feng Shui beliefs.