def changeWidgetColor(pageIndex, columnIndex, widgetIndex, color, retJson=True
    ):
    """ change color of widget.

        @param pageIndex
        index of page the widget lies on( start from 0 )

        @param columnIndex
        index of column the widget lies on( start from 0 )

        @param widgetIndex
        index of the widget, count from top to bottom( start from 0 )

        @param color
        widget color

        @retJson
        format return value to json format or not( default True )

        @return
        a dict contains state of process, format like:
        {
            'success': True,
            'msg': 'Change widget color success.'
        }

        """
