Most wall surfaces are drywall covered by toxic paint. Some are fancier, sporting traditional plaster that's textured -- "hand-troweled" -- for a rustic look or mixed with pigment for a Venetian or Moroccan look.
They're custom, high-end finishes that add real interest and value to a home. The problem, from an environmental perspective, is that these plasters are typically gypsum-based, and manufacturing them has a high carbon footprint. Plus, some of the brighter pigments can contain volatile organic compounds.
A relatively new product has solved the biggest of plaster's green issues. Natural plaster, or "Earth plaster," avoids the gypsum, allowing it to be manufactured at lower temperatures. This decreases the CO2 emissions associated with the process.
The most Earth-friendly (and fume-free) Earth plaster is unpigmented, going on in natural Earth tones and often textured for an organic look. If pigments are used, VOCs can still be a problem, so make sure you (or your contractor) go with nontoxic coloring agents. Earth clay also comes in paint form, which is zero-VOC.