Aplicar gradiente em um Icon no Futter

icon_gradient.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: RadiantGradientMask(
            child: Icon(
              Icons.book,
              size: 250,
              color: Colors.white,
            ),
          ),
        ),
      ),
    );
  }
}

class RadiantGradientMask extends StatelessWidget {
  RadiantGradientMask({this.child});
  final Widget child;

  @override
  Widget build(BuildContext context) {
    return ShaderMask(
      shaderCallback: (bounds) => RadialGradient(
        center: Alignment.center,
        radius: 0.5,
        colors: [Colors.blue, Colors.red],
        tileMode: TileMode.mirror,
      ).createShader(bounds),
      child: child,
    );
  }
}