/**
* Get #ffffff html hex number for a colour
*
* @see #toHexString(int)
* @param c
*        Color object whose html colour number you want as a string
* @return # followed by exactly 6 hex digits
*/
public final static String toString ( Color c )
   {
   String s = Integer.toHexString( c.getRGB() & 0xffffff );
   if ( s.length() < 6 )
      { // pad on left with zeros
      s = "000000".substring( 0, 6 - s.length() ) + s;
      }
   return '#' + s;
   }