Detect if iOS13 Dark Mode is enabled from Flutter/Dart

Yes it is possible. Look here https://github.com/flutter/flutter/issues/33873#issuecomment-536309491 and here is the answer.

if(ios13==true){
    bool qDarkmodeEnable;
    var qdarkMode = MediaQuery.of(context).platformBrightness;
    if (qdarkMode == Brightness.dark){
        qDarkmodeEnable=true;
    } else {
        qDarkmodeEnable=false;
    }
}

Here's how you can set different colors for light and dark mode, the app will automatically switch if the phone is set to dark mode or light mode.

MaterialApp(
  theme: ThemeData(
    brightness: Brightness.light,
    primaryColor: Colors.red,
  ),
  darkTheme: ThemeData(
    brightness: Brightness.dark,
    // additional settings go here
  ),
);

::Update::

You can also get the platform brightness (Brightness.light / Brightness.dark) using

WidgetsBinding.instance.window.platformBrightness

but you will have to use the WidgetsBindingObserver mixin and override the method below

@override
void didChangePlatformBrightness() {
    print(WidgetsBinding.instance.window.platformBrightness); // should print Brightness.light / Brightness.dark when you switch
    super.didChangePlatformBrightness(); // make sure you call this
}

see https://api.flutter.dev/flutter/widgets/WidgetsBindingObserver-class.html on how to use the mixin.