there is a wrong place here, http://learn.jquery.com/plugins/basic-plugin-creation/

[liuwuyue]

(function ( $ ) {

$.greenify = function( options ) {

// This is the easiest way to have default options.
var settings = $.extend({
  "color": "#556B2F",  // These are the defaults
  "background-color": "white"
}, options );

// Greenify the collection based on the settings variable
return this.css({
  "color": settings.color,
  "background-color": settings.background-color
});

};
}( jQuery ));

$("div").greenify({
"color": "orange"
});

here , it should be $.fn.greenify