Refine milky Dock and refract symbols beneath the moving lens

mobile/test/widgets/glass_dock_test.dart

@@ -9,6 +9,58 @@ import 'navigation_test.dart' show uiController;
 
 void main() {
   setUpAll(tzdata.initializeTimeZones);
+  testWidgets('only the selected tab is blue, including during glass travel', (
+    tester,
+  ) async {
+    var selected = 0;
+    await tester.pumpWidget(
+      MaterialApp(
+        home: StatefulBuilder(
+          builder: (context, setState) => Scaffold(
+            body: Center(
+              child: GlassDock(
+                selectedIndex: selected,
+                onSelected: (index) => setState(() => selected = index),
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+    Color colour(IconData icon) =>
+        tester.widget<Icon>(find.byIcon(icon)).color!;
+    void expectGrey(IconData icon) {
+      final value = colour(icon);
+      expect((value.r - value.b).abs(), lessThan(0.12));
+      expect(value.a, 1);
+    }
+
+    expect(colour(Icons.calendar_month_rounded), const Color(0xFF007AFF));
+    expectGrey(Icons.assignment_rounded);
+    expectGrey(Icons.person_rounded);
+    await tester.tap(find.byIcon(Icons.person_rounded));
+    await tester.pump();
+    // Colour follows the selected page, not whichever icon the lens crosses.
+    expect(colour(Icons.person_rounded), const Color(0xFF007AFF));
+    expectGrey(Icons.calendar_month_rounded);
+    await tester.pump(const Duration(milliseconds: 100));
+    expectGrey(Icons.assignment_rounded);
+    await tester.pumpAndSettle();
+    final gesture = await tester.startGesture(
+      tester.getCenter(find.byKey(const Key('dock-cursor'))),
+    );
+    await gesture.moveBy(const Offset(-20, 0));
+    await tester.pump();
+    await gesture.moveBy(const Offset(-90, 0));
+    await tester.pump(const Duration(milliseconds: 150));
+    expect(colour(Icons.person_rounded), const Color(0xFF007AFF));
+    expectGrey(Icons.assignment_rounded);
+    await gesture.up();
+    await tester.pumpAndSettle();
+    expect(selected, 1);
+    expect(colour(Icons.assignment_rounded), const Color(0xFF007AFF));
+    expectGrey(Icons.person_rounded);
+  });
   testWidgets('dock drags switch tabs while body swipes only change week', (
     tester,
   ) async {