Update hintColor value for Material (#65036)

packages/flutter/lib/src/material/theme_data.dart

@@ -332,7 +332,7 @@ class ThemeData with Diagnosticable {
     backgroundColor ??= isDark ? Colors.grey[700] : primarySwatch[200];
     dialogBackgroundColor ??= isDark ? Colors.grey[800] : Colors.white;
     indicatorColor ??= accentColor == primaryColor ? Colors.white : accentColor;
-    hintColor ??= isDark ? const Color(0x80FFFFFF) : const Color(0x8A000000);
+    hintColor ??= isDark ? Colors.white60 : Colors.black.withOpacity(0.6);
     errorColor ??= Colors.red[700];
     inputDecorationTheme ??= const InputDecorationTheme();
     pageTransitionsTheme ??= const PageTransitionsTheme();