Most ceramic colors sit on the surface of the clay.
This method is fairly new. It was pioneered in the late eighties by the Nowegian Professor of Ceramics Arne Aase, and there are still relatively few people using it. This may be in part due to the high toxicity of most of the chemicals in their raw state and partly due to their prohibitive cost. In my forms I strive for simplicity and subtlety. I actually only use variations of two or three basic bowl, vase or beaker forms.