custom_scrollview.dart

import 'package:flutter/material.dart';

void main() => runApp(new MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'My Flutter Pad'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

const kExpandedHeight = 300.0;

class _MyHomePageState extends State<MyHomePage> {
  ScrollController _scrollController;

  @override
  void initState() {
    super.initState();

    _scrollController = ScrollController()
      ..addListener(() => setState(() {}));
  }

  bool get _showTitle {
    return _scrollController.hasClients
        && _scrollController.offset > kExpandedHeight - kToolbarHeight;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: CustomScrollView(
        controller: _scrollController,
        slivers: <Widget>[
          SliverAppBar(
            pinned: true,
            leading: IconButton(icon: Icon(Icons.menu), onPressed: () {},),
            expandedHeight: kExpandedHeight,
            title: _showTitle ? Text('_SliverAppBar') : null,
            flexibleSpace: _showTitle ? null : FlexibleSpaceBar(
              title: new Column(
                mainAxisAlignment: MainAxisAlignment.end,
                children: <Widget>[
                  Text('_SliverAppBar'),
                  Text('subtitle'),
                ],
              ),
              background: Column(
                mainAxisAlignment: MainAxisAlignment.center,
                children: <Widget>[
                  Text('Info'),
                ],
              ),
            ),
          ),
          SliverList(
            delegate: SliverChildListDelegate(List<Text>.generate(100, (int i) {
              return Text("List item $i");
            })),
          ),
        ]
      ),
    );
  }
}

Excellent demo. but using ..addListener(() => setState(() {})); Does do like this will have bad effect on performance?
Making _showTitle as a property, adding a condition to call setState method, will it be better?
like this The way I thought

Not sure about performance (would have to be measured), but it's definitely not recommended by the community to call an empty setState.
I've extracted this piece of code from a widget of mine a long time ago, so I could have a reference whenever I needed. However, the widget in question was also doing a parallax and I was just getting started with flutter.
Your example is really better and I recommend anyone with a use case like this to use it.

I already try this,Anyway nice demo.
But i have some question, Why everytime i scrolled my listview always refresh. I assume this script make my listview always refresh every scrolled. And make my app very slow.

_scrollController = ScrollController()
      ..addListener(() => setState(() {}));
  }

import 'package:cached_network_image/cached_network_image.dart';
import 'package:flutter/material.dart';
import 'package:flutter_news/api/Api_news.dart';
import 'package:flutter_news/pages/display_json/FetchNewsByWartawan.dart';
import 'package:flutter_news/pages/reusableWidget/DataNotFound.dart';
import 'package:flutter_news/pages/reusableWidget/LoadingIndicator.dart';

import 'package:flutter_screenutil/flutter_screenutil.dart';

class WartawanDetail extends StatefulWidget {
  final int idWartawan;
  final String gambarWartawan;
  final String namaWartawan;
  final int jumlahBerita;
  WartawanDetail({
    this.idWartawan,
    this.gambarWartawan,
    this.namaWartawan,
    this.jumlahBerita,
  });
  @override
  _WartawanDetailState createState() => _WartawanDetailState();
}

class _WartawanDetailState extends State<WartawanDetail> {
  ScrollController _scrollController;
  ApiHelper api = ApiHelper();
  @override
  void initState() {
    super.initState();
    _scrollController = ScrollController()
      ..addListener(() => setState(() {
            print("${_scrollController.offset}");
          }));
  }

  bool get _changeColor {
    return _scrollController.hasClients &&
        _scrollController.offset > (250 - kToolbarHeight);
  }

  @override
  Widget build(BuildContext context) {
    return SafeArea(
      top: true,
      child: Scaffold(
        body: CustomScrollView(
          controller: _scrollController,
          slivers: <Widget>[
            SliverAppBar(
              floating: false,
              pinned: true,
              expandedHeight: ScreenUtil.getInstance().setHeight(250),
              leading: Container(
                child: IconButton(
                  icon: Icon(
                    Icons.arrow_back,
                    color: _changeColor ? Colors.blue : Colors.black,
                  ),
                  onPressed: () => Navigator.pop(context),
                ),
              ),
              flexibleSpace: FlexibleSpaceBar(
                title: Container(
                  child: Text(widget.namaWartawan),
                ),
                background: Container(
                  child: CachedNetworkImage(
                    fit: BoxFit.cover,
                    imageUrl:
                        "${Urls.BASE_API_IMAGE}/wartawan/${widget.gambarWartawan}",
                  ),
                ),
              ),
              actions: <Widget>[
                IconButton(
                  icon: Icon(Icons.more_horiz),
                  onPressed: () => "",
                ),
              ],
            ),
            SliverFixedExtentList(
              itemExtent: MediaQuery.of(context).size.height,
              delegate: SliverChildListDelegate(
                [
                  Container(
                    padding: EdgeInsets.all(8),
                    child: FutureBuilder(
                      future: api.getBeritaByWartawan(widget.idWartawan),
                      builder: (BuildContext context, AsyncSnapshot snapshot) {
                        switch (snapshot.connectionState) {
                          case ConnectionState.waiting:
                          case ConnectionState.active:
                            return LoadingIndicator();
                            break;
                          default:
                            if (!snapshot.hasData) {
                              return DataNotFound();
                            } else {
                              return ListView.builder(
                                shrinkWrap: true,
                                physics: NeverScrollableScrollPhysics(),
                                itemCount: snapshot.data.length,
                                itemBuilder: (BuildContext context, int index) {
                                  return FetchNewsByWartawan(
                                    idBerita: snapshot.data[index].idBerita,
                                    judulBerita:
                                        snapshot.data[index].judulBerita,
                                    isiBerita: snapshot.data[index].isiBerita,
                                    namaKategori:
                                        snapshot.data[index].namaKategori,
                                    namaWartawan:
                                        snapshot.data[index].namaWartawan,
                                    tanggalBerita:
                                        snapshot.data[index].tanggalBerita,
                                    gambarBerita:
                                        snapshot.data[index].gambarBerita,
                                  );
                                },
                              );
                            }
                        }
                      },
                    ),
                  ),
                ],
              ),
            )
          ],
        ),
      ),
    );
  }
}

@zgramming you will maybe have better luck following @fattiger00's gist. Your widget just needs to rebuild when the colour will in fact change. Maybe putting the scroll logic and list logic in separate widgets would be wise.