code: private String rgbColorStr(Color c) {
          StringBuilder b = new StringBuilder("rgb(");
          b.append(c.getRed()).append(",").append(c.getGreen()).append(",")
                  .append(c.getBlue()).append(")");
          return b.toString();
      }
docs: Returns the SVG RGB color string for the specified color.
  
  @param c  the color ({@code null} not permitted).
  
  @return The SVG RGB color string.