An example that uses raw dart:ui to fill the screen with green color

raw_dart_ui.dart

import 'dart:ui';

void main() {
  var recorder = PictureRecorder();
  var canvas = Canvas(recorder, Rect.largest);
  canvas.drawColor(const Color(0xFF00FF00), BlendMode.srcOver);
  var picture = recorder.endRecording();
  var sceneBuilder = SceneBuilder();
  sceneBuilder.addPicture(Offset.zero, picture);
  var scene = sceneBuilder.build();
  window.render(scene);
}