你可以像下面这样使用iconTheme:

iconTheme: IconThemeData(
  color: Colors.black, // <= You can change your color here.
),

在AppBar中，添加前导参数并分配BackButton小部件。然后将颜色参数添加到BackButton，如下所示:

AppBar(
  leading: const BackButton(
    color: Colors.black, // Change the color here
  ),
  centerTitle: true,
)

要自定义引导图标，您可能需要模仿AppBar小部件的功能，该小部件根据当前上下文正确地处理显示后退按钮、抽屉图标或关闭图标。下面是一个替换默认图标的例子。

import 'package:flutter/material.dart';

class TopBar extends StatelessWidget with PreferredSizeWidget {
  static const double _topBarHeight = 60;

  @override
  Widget build(BuildContext context) {
    return AppBar(
      toolbarHeight: _topBarHeight,
      title: Text('Title'),
      automaticallyImplyLeading: false,
      leading: _buildLeadingWidget(context),
    );
  }

  @override
  Size get preferredSize => Size.fromHeight(_topBarHeight);

  Widget _buildLeadingWidget(BuildContext context) {
    final ScaffoldState scaffold = Scaffold.of(context);
    final ModalRoute<dynamic> parentRoute = ModalRoute.of(context);

    final bool canPop = ModalRoute.of(context)?.canPop ?? false;
    final bool hasDrawer = scaffold?.hasDrawer ?? false;
    final bool useCloseButton = parentRoute is PageRoute<dynamic> && parentRoute.fullscreenDialog;

    Widget leading;
    if (hasDrawer) {
      leading = IconButton(
        icon: const Icon(Icons.menu_rounded),
        onPressed: Scaffold.of(context).openDrawer,
        tooltip: MaterialLocalizations.of(context).openAppDrawerTooltip,
      );
    } else {
      if (canPop) {
        if (useCloseButton) {
          leading = IconButton(
              color: Theme.of(context).colorScheme.onBackground,
              icon: Icon(Icons.close_rounded),
              onPressed: () => Navigator.of(context).maybePop());
        } else {
          leading = IconButton(
              padding: EdgeInsets.all(0),
              iconSize: 38,
              icon: Icon(Icons.chevron_left_rounded),
              onPressed: Navigator.of(context).pop);
        }
      }
    }

    return leading;
  }
}

这个类使用PreferredSizeWidget作为一个mixin，因此您可以使用它来替换脚手架中现有的AppBar小部件。请注意_buildLeadingWidget方法，它只在必要时显示后退按钮，如果有抽屉，则显示菜单按钮，如果显示全屏对话框，则显示关闭按钮。

你可以像下面这样使用iconTheme:

iconTheme: IconThemeData(
  color: Colors.black, // <= You can change your color here.
),

你也可以为应用程序设置领先的图标颜色

MaterialApp(
  theme: ThemeData(
    appBarTheme: AppBarTheme(
      iconTheme: IconThemeData(
        color: Colors.green
      )
    )
  )
)

你必须使用AppBar中的iconTheme属性，像这样:

appBar: AppBar(
  iconTheme: IconThemeData(
    color: Colors.black, //change your color here
  ),
  title: Text("Sample"),
  centerTitle: true,
),

或者你想自己操作后退按钮。

appBar: AppBar(
  leading: IconButton(
    icon: Icon(Icons.arrow_back, color: Colors.black),
    onPressed: () => Navigator.of(context).pop(),
  ), 
  title: Text("Sample"),
  centerTitle: true,
),

更好的是，只有当你想改变后退按钮的颜色时才可以这样做。

appBar: AppBar(
  leading: BackButton(
     color: Colors.black
   ), 
  title: Text("Sample"),
  centerTitle: true,
),