public _alpha : Number

The alpha transparency value of the button specified by my_btn. Valid values are 0 (fully transparent) to 100 (fully opaque). The default value is 100. Objects in a button with _alpha set to 0 are active, even though they are invisible.

Example

The following code sets the _alpha property of a button named myBtn_btn to 50% when the user clicks the button. First, add a Button instance on the Stage. Second, give it an instance name of myBtn_btn. Lastly, with frame 1 selected, place the following code into the Actions panel:

myBtn_btn.onRelease = function(){
    this._alpha = 50;
};

See also

_alpha (MovieClip._alpha property), _alpha (TextField._alpha property)