Could it also work with bump mapping and transparency, and have a shader that turns completely invisible when it's not lighted (thus showing the black on the main body of the fish), but when it is, only the specular appears (varying its color from yellow to indigo)?Look up ramp and facing angle I think that would work, you might have to model the scales of the fish to make it work.................dave
More like a combo of both probably.So wait, are you trying to control the color based on how much light is hitting the surface or how its facing the camera? You could use the surface luminance node or the sampler info node, respectively.