Future<List> _getColors() async {
  Color gradientOne, gradientTwo;
  String imageUrl = json['image'];

  paletteGenerator = await PaletteGenerator.fromImageProvider(
      CachedNetworkImageProvider(imageUrl));

  gradientOne = paletteGenerator.colors.toList()[0];
  gradientTwo = paletteGenerator.colors.toList()[1];

  return [gradientOne, gradientTwo];
}

post.gradientColors
    .then((result) => {
          gradient = result,
          this.setState(() {
                  loading = false;
                })
        })

List<Future> futures = [];

  for (var post in tmpList) {
    futures.add(post.gradientColors);
  }
  await Future.wait(futures)
      .then((result) => {list.addAll(tmpList)});
}