Ease alpha with hittest

hey. im using the hittest code from senocular to make a menu fade out. it’s working but i was wondering if someone could explain how i could add ease to the alpha. i’ve tried implementing some of the ease codes found on here but havn’t had any luck. thanks.

black.isPressed = false; // flag
black.isOver = false; // flag

black.onMouseMove = function(){
    var lastIsOver = this.isMouseOver;
    if (this.hitTest(_root._xmouse, _root._ymouse, true)) {
        this.isMouseOver = true;
        if (this.isMouseOver != lastIsOver){
            if (this.isPressed){
                this._alpha = 0;
            }else{
                this._alpha = 0;
            }
        }
    }else{
        this.isMouseOver = false;
        if (this.isMouseOver != lastIsOver){
            if (this.isPressed){
                this._alpha += 90;
            }else{
                this._alpha += 90;
            }
        }
    }
}