code: public void setColorRange(int firstIndex, int lastIndex, int color1, int color2) {
  		for (int i = firstIndex; i <= lastIndex; i++)
  			map[i] = ImageMath.mixColors((float)(i-firstIndex)/(lastIndex-firstIndex), color1, color2);
  	}
docs: Set a range of the colormap, interpolating between two colors.
  @param firstIndex the position of the first color
  @param lastIndex the position of the second color
  @param color1 the first color
  @param color2 the second color