anchor.diff:  
           final double zLen = zmax - zmin;
   
  -        for (int i = 0; i < numPoints * 3; i += 3) {
  +        for (int i = 0, j = 0; i < numPoints * 3; i += 3, j += 4) {
               double z = positions[i + 2];
               double scaledZ = (z - zmin) / zLen;
   
  
positive.code:             }
              assert(result != null);
  
              newColors[i + 0] = result.r / 255.0;
              newColors[i + 1] = result.g / 255.0;
              newColors[i + 2] = result.b / 255.0;
          }
  
          return newColors;
  
negative.code:                 newColors[i + 1] = 0.0;
                  newColors[i + 2] = (c - 0.6666) * 3.0;
              }
              newColors[i + 3] = 1.0;
          }
  
          return newColors;
  