如何在flutter中动态更改InputDecoration的fillColor？

import 'package:flutter/material.dart';

class MyInputField extends StatefulWidget {
  @override
  _MyInputFieldState createState() => _MyInputFieldState();
}

class _MyInputFieldState extends State<MyInputField> {
  Color _fillColor = Colors.white; // 初始填充颜色为白色

  void changeFillColor(Color color) {
    setState(() {
      _fillColor = color;
    });
  }

  @override
  Widget build(BuildContext context) {
    return TextFormField(
      decoration: InputDecoration(
        fillColor: _fillColor,
        filled: true,
        border: OutlineInputBorder(),
      ),
    );
  }
}

MyInputField inputField = MyInputField();
inputField.changeFillColor(Colors.blue); // 更改填充颜色为蓝色