Here's a photo of my rockface waterfall. I made this with a 40mm foam cladding board, the standard basecoat acrylic cement render and fibreglass mesh, then layers of different mixtures of decomposed granite cement and iron oxide. It's really hard to get good colours using iron oxide, even though the powered stuff looks fantastic, the cement seems to dull the colour. Being wet improves the look considerably, and though you can't really see in this photo, there is some baby moss just developing in the little cracks in the surface giving everything a speckled green look. The black is some kind of bacteria or algae that breaks down nutrients in the water. It only grows where there is constant water flowing, the moss prefers areas that wet and dry cyclicly. The decomposed granite not only brings in texture, but I have scrubbed the surface back to the crystals of feldspars and quartz, giving the surface a glittery look in the sun.
There are multiple reasons for the rockface. Having water fall through the air increases the humidity whilst cooling the air. The large surface area of splashing water increases the evaporation rate. We could control the cooling effect by adjusting the fresh air flow from outside or by regulating the flow rate. I have two separately controled supplies to the rockface, one that spreads a thin film over part of the surface (as shown here), and one that produces a large splashing flow. Eventually I'll have computer controlled flow rates.
A second purpose of the rockface is to purify the water. The water flows over a biological surface, and the rough surface provides lots of niches for different species.
Finally, it looks better than a painted wall.