SetGray()

         Creates a virtual b/w monitor

    Syntax:

         SetGray( lGray ) -> Nil

         lGray : a logic value indicating if you want a virtual b/w monitor

    Description:

         This function allows your programs to run simulating a b/w
         monitor.
         It's very useful if you want test your programs with a b/w monitor.

    Return:

         Nothing.

    Example:

         cPalette := GetPalette()
         SetGray( .T. )
         BoxWarning( "The monitor is b/w!!!" )
         SetGray( .F. )
         SetPalette( cPalette )
         BoxWarning( "The monitor is color!!!, of course" )