code: public static ImageOption backgroundColorOf(int color) {
      if (color < 0 || color > 0xFFFFFF) {
        throw new IllegalArgumentException("Color must be in rgb hex range of 0x0 to 0xFFFFFF.");
      }
      return new ImageOption("bg", "rgb:" + format(Locale.getDefault(), "%06X", color));
    }
docs: Define a background color.
  <p>
  The color value must be a hexadecimal value, i.e. 0xFF0000 means red.
  
  @param color the color in hex to be used.
  @return an image option for manipulating a given url.
  @throws IllegalArgumentException if the color is less then zero or greater then 0xFFFFFF.