animation-controller.dart

Color gradientStartFrom = Colors.deepPurple;
Color gradientStartTo = Colors.purple;
Color gradientEndFrom = new Color(0xff483475);
Color gradientEndTo = new Color(0xff070B34);

animControlStar = new AnimationController(vsync: this, duration: new Duration(milliseconds: 2000));

fadeAnimStar1 = new Tween(begin: 0.0, end: 1.0)
        .animate(new CurvedAnimation(parent: animControlStar, curve: new Interval(0.0, 0.5)));
fadeAnimStar1.addListener(() {
      setState(() {});
});

colorAnimBgStart = new ColorTween(begin: gradientStartFrom, end: gradientStartTo).animate(animControlBg);
colorAnimBgEnd = new ColorTween(begin: gradientEndFrom, end: gradientEndTo).animate(animControlBg);

animControlStar.addStatusListener((status) {
      if (status == AnimationStatus.completed) {
        animControlStar.reverse();
      } else if (status == AnimationStatus.dismissed) {
        animControlStar.forward();
      }
});