Flutter - How do I toggle the color of a FlatButton upon click?

Question

I want to change the color when the FlatButton is pressed. Thanks for your help.

import 'package:flutter/material.dart';

class ButtonCalculate extends StatelessWidget {

@override
Widget build(BuildContext context) {
var container = Container(
  decoration: BoxDecoration(gradient: null,
  borderRadius: BorderRadius.circular(20.0),
  //color: Colors.amber,
  boxShadow: [
    BoxShadow(
      color: Colors.black12,
      offset: Offset(0.0, 0.5),
      blurRadius: 40.5,
    ),
  ]),
  child: new FlatButton(
    child: Image(
      image:AssetImage('assets/2.0x/Button_Calculate.png')),
    onPressed: () {},
  ),
  width: 290.0,
);

Answer 1

I want to change the color when the FlatButton is pressed. Thanks for your help.

import 'package:flutter/material.dart';

class ButtonCalculate extends StatelessWidget {

@override
Widget build(BuildContext context) {
var container = Container(
  decoration: BoxDecoration(gradient: null,
  borderRadius: BorderRadius.circular(20.0),
  //color: Colors.amber,
  boxShadow: [
    BoxShadow(
      color: Colors.black12,
      offset: Offset(0.0, 0.5),
      blurRadius: 40.5,
    ),
  ]),
  child: new FlatButton(
    child: Image(
      image:AssetImage('assets/2.0x/Button_Calculate.png')),
    onPressed: () {},
  ),
  width: 290.0,
);