Radial Shader Code

shader
SEM_Radial(    float innerR = 0,
           float outerR = 2,
           color innerC = color(1,0,0),
           color outerC = color(0,1,0),
           string spacename = "object",
          output color resultRGB = 0)
{
point p = transform(spacename, P);
float dist = distance(point(0,0,0), p);
float blend = smoothstep(innerR, outerR, dist);
resultRGB = mix(innerC, outerC, blend);
}