Examples: replace blue with more ObjectBox-like teal color

Author: greenrobot-team

objectbox/example/flutter/objectbox_demo/lib/main.dart

@@ -26,7 +26,7 @@ class MyApp extends StatelessWidget {
   @override
   Widget build(BuildContext context) => MaterialApp(
         title: 'OB Example',
-        theme: ThemeData(primarySwatch: Colors.blue),
+        theme: ThemeData(primarySwatch: Colors.teal),
         home: const MyHomePage(title: 'OB Example'),
       );
 }

objectbox/example/flutter/objectbox_demo_relations/lib/main.dart

@@ -28,7 +28,7 @@ class MyApp extends StatelessWidget {
   @override
   Widget build(BuildContext context) => MaterialApp(
         title: 'Task-list app example',
-        theme: ThemeData(primarySwatch: Colors.blue),
+        theme: ThemeData(primarySwatch: Colors.teal),
         home: const MyHomePage(title: 'ObjectBox Example'),
       );
 }

objectbox/example/flutter/objectbox_demo_relations/lib/task_elements.dart

@@ -79,7 +79,7 @@ class _TaskInputState extends State<TaskInput> {
                     items: tags.map(buildMenuItem).toList(),
                     underline: Container(
                       height: 2,
-                      color: Colors.blueAccent,
+                      color: Theme.of(context).colorScheme.primary,
                     ),
                     onChanged: (value) => {
                           setState(

objectbox/example/flutter/objectbox_demo_sync/lib/main.dart

@@ -26,7 +26,7 @@ class MyApp extends StatelessWidget {
   @override
   Widget build(BuildContext context) => MaterialApp(
         title: 'OB Example (sync)',
-        theme: ThemeData(primarySwatch: Colors.blue),
+        theme: ThemeData(primarySwatch: Colors.teal),
         home: const MyHomePage(title: 'OB Example (sync)'),
       );
 }