Change color of Theme - flutter

Question

I wanted to change the color of the counter in my app. I want to do that: change the color of the counter to blue when counter bigger than 0. if counter smaller than 0 change the color of the counter to red.if counter equal to 0 change the color of the counter to green. is it possible? I did just for 2 colors.
it is my codes :
import 'package:flutter/material.dart';
void main() {
runApp(Myapp());
}
class Myapp extends StatefulWidget {
#override
_MyappState createState() => _MyappState();
}
class _MyappState extends State<Myapp> {
#override
Widget build(BuildContext context) {
// TODO: implement build
return MaterialApp(
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: Myhomepage(
title: "My Home Page",
),
);
}
}
class Myhomepage extends StatefulWidget {
final String title;
Myhomepage({this.title});
#override
_MyhomepageState createState() => _MyhomepageState();
}
class _MyhomepageState extends State<Myhomepage> {
int counter = 0;
#override
Widget build(BuildContext context) {
// TODO: implement build
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
centerTitle: true,
),
floatingActionButton: FloatingActionButton(
child: Icon(Icons.add),
backgroundColor: Colors.grey[850],
onPressed: () {
setState(() {
counter++;
});
}),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
RaisedButton(
child: Text(
"Increase",
),
color: Colors.green,
onPressed: () {
setState(() {
counter++;
});
},
),
Text("The count of press button:"),
Text(
"$counter",
style: Theme.of(context).textTheme.display2.copyWith(color: counter<=0 ? Colors.red : Colors.blue)
),
RaisedButton(
child: Text(
"Decrease",
),
color: Colors.red,
onPressed: () {
setState(() {
counter--;
});
},
),
],
),
),
);
}
}
it is my results :

Answer 1

Here's one way you can implement the system you want. I just made a function that returns the desired color.
class _MyhomepageState extends State<Myhomepage> {
int counter = 0;
Color _getCounterColor() {
if (counter > 0) return Colors.blue;
else if (counter < 0) return Colors.red;
else return Colors.green;
}
#override
Widget build(BuildContext context) {
// TODO: implement build
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
centerTitle: true,
),
floatingActionButton: FloatingActionButton(
child: Icon(Icons.add),
backgroundColor: Colors.grey[850],
onPressed: () {
setState(() {
counter++;
});
}),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
RaisedButton(
child: Text(
"Increase",
),
color: Colors.green,
onPressed: () {
setState(() {
counter++;
});
},
),
Text("The count of press button:"),
Text(
"$counter",
style: Theme.of(context).textTheme.display2.copyWith(color: _getCounterColor()),
),
RaisedButton(
child: Text(
"Decrease",
),
color: Colors.red,
onPressed: () {
setState(() {
counter--;
});
},
),
],
),
),
);
}
}