You can make your bathroom like a steamy sauna simply using frosted glass in the shower or around the lining of the wall. Frosted glass can be a motif throughout the room--the shower door can use frosted glass, as can the edges of the mirror by the sink, and the windows if you have any. It gives you a level of privacy, but also works well with steam. It looks like some paradise getaway sauna. You can emphasize this with bath accessories like natural pumice skin treatment and sea sponge loofas, etc.
If you prefer you can use a brown bathroom mosaic tile and give your bathroom a modern visual element. Brown is an earthy tone and it's very neutral. It can be paired with both light and dark colors to complete a palette. You can even pair the dark glass bathroom tiles with stone for accent marks around the room or in the shower.
Also, the natural-looking tiles go nice with nickel, brass, and steel fixtures. The metal and natural combination works really well to keep your home looking sleek and clean. Make sure you buy fixtures that have water conserving features.
Ceramic and other clay-based tiles are also very natural. They're a bit sleeker and can be used on the wall with a stone or shimmering glass floor for a very modern take on a natural theme. If you're trying for a burst of color rather than the earthy tones, look for other naturally occurring colors-- perhaps sunny yellow, coral pink, and sea green? You can make your bathroom a beach house escape. Add in a few sea-salts by the bath and seashell holding trays for emphasis.
These are just a few ideas to help drive your imagination while staying eco-friendly and incorporating natural elements into your home design, especially into the bathroom. Feel free to go looking for inspiration in magazines, in stores, or even maybe just a walk outside for fresh air. Take what you see and bring it back with you, if not literally then through a mental note.