/* $DOC$
   $NAME$
      ft_InvClr()
   $CATEGORY$
      Conversion
   $ONELINER$
      Get the inverse of a color
   $SYNTAX$
      ft_InvClr( [ <cDsrdColor> ] ) -> cColor
   $ARGUMENTS$
      <cDsrdColor> is the color to get the inverse of.  Defaults to
      current color.
   $RETURNS$
      The inverse of the passed color.
   $DESCRIPTION$
      This function inverts a passed color (in the Clipper format: ??/??),
      e.g., "W/N" is converted to "N/W".
   $EXAMPLES$
      ? ft_InvClr()             // Get Inverse of Current Color
      ? ft_InvClr( cErrColor )  // Get Inverse of cErrorColor
   $END$
 */