Update Dark Theme disabledColor to White38 (#35136)

* Add Colors.white38

* Update ThemeData.disabledColor and ButtonThemeData.disabledColor to Colors.white38

* Update pre-existing tests to expect Colors.white38 instead of Colors.white30

* Update API documentation to reflect these changes

examples/stocks/test/icon_color_test.dart

@@ -85,7 +85,7 @@ void main() {
 
     // check the color of the icon - dark mode
     checkIconColor(tester, 'Stock List', Colors.redAccent); // theme accent color
-    checkIconColor(tester, 'Account Balance', Colors.white30); // disabled
+    checkIconColor(tester, 'Account Balance', Colors.white38); // disabled
     checkIconColor(tester, 'About', Colors.white); // enabled
   });
 }

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

@@ -468,18 +468,12 @@ class ButtonThemeData extends Diagnosticable {
     return button.textTheme ?? textTheme;
   }
 
-  Color _getDisabledColor(MaterialButton button) {
-    return getBrightness(button) == Brightness.dark
-      ? colorScheme.onSurface.withOpacity(0.30)  // default == Colors.white30
-      : colorScheme.onSurface.withOpacity(0.38); // default == Colors.black38;
-  }
-
   /// The foreground color of the [button]'s text and icon when
   /// [MaterialButton.onPressed] is null (when MaterialButton.enabled is false).
   ///
   /// Returns the button's [MaterialButton.disabledColor] if it is non-null.
   /// Otherwise the color scheme's [ColorScheme.onSurface] color is returned
-  /// with its opacity set to 0.30 if [getBrightness] is dark, 0.38 otherwise.
+  /// with its opacity set to 0.38.
   ///
   /// If [MaterialButton.textColor] is a [MaterialStateProperty<Color>], it will be
   /// used as the `disabledTextColor`. It will be resolved in the [MaterialState.disabled] state.
@@ -488,7 +482,7 @@ class ButtonThemeData extends Diagnosticable {
       return button.textColor;
     if (button.disabledTextColor != null)
       return button.disabledTextColor;
-    return _getDisabledColor(button);
+    return colorScheme.onSurface.withOpacity(0.38);
   }
 
   /// The [button]'s background color when [MaterialButton.onPressed] is null
@@ -500,13 +494,13 @@ class ButtonThemeData extends Diagnosticable {
   /// is returned, if it is non-null.
   ///
   /// Otherwise the color scheme's [ColorScheme.onSurface] color is returned
-  /// with its opacity set to 0.3 if [getBrightness] is dark, 0.38 otherwise.
+  /// with its opacity set to 0.38.
   Color getDisabledFillColor(MaterialButton button) {
     if (button.disabledColor != null)
       return button.disabledColor;
     if (_disabledColor != null)
       return _disabledColor;
-    return _getDisabledColor(button);
+    return colorScheme.onSurface.withOpacity(0.38);
   }
 
   /// The button's background fill color or null for buttons that don't have

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

@@ -303,7 +303,7 @@ class Colors {
   ///  * [Typography.white], which uses this color for its text styles.
   ///  * [Theme.of], which allows you to select colors from the current theme
   ///    rather than hard-coding colors in your build methods.
-  ///  * [white70, white60, white54, white30, white12, white10], which are variants on this color
+  ///  * [white70, white60, white54, white38, white30, white12, white10], which are variants on this color
   ///    but with different opacities.
   ///  * [black], a solid black color.
   ///  * [transparent], a fully-transparent color.
@@ -320,7 +320,7 @@ class Colors {
   ///  * [Typography.white], which uses this color for its text styles.
   ///  * [Theme.of], which allows you to select colors from the current theme
   ///    rather than hard-coding colors in your build methods.
-  ///  * [white, white60, white54, white30, white12, white10], which are variants on this color
+  ///  * [white, white60, white54, white38, white30, white12, white10], which are variants on this color
   ///    but with different opacities.
   static const Color white70 = Color(0xB3FFFFFF);
 
@@ -336,7 +336,7 @@ class Colors {
   ///  * [ExpandIcon], which uses this color for dark themes.
   ///  * [Theme.of], which allows you to select colors from the current theme
   ///    rather than hard-coding colors in your build methods.
-  ///  * [white, white54, white30, white12, white10], which are variants on this color
+  ///  * [white, white54, white30, white38, white12, white10], which are variants on this color
   ///    but with different opacities.
   static const Color white60 = Color(0x99FFFFFF);
 
@@ -348,11 +348,11 @@ class Colors {
   ///
   ///  * [Theme.of], which allows you to select colors from the current theme
   ///    rather than hard-coding colors in your build methods.
-  ///  * [white, white60, white30, white12, white10], which are variants on this color
+  ///  * [white, white60, white38, white30, white12, white10], which are variants on this color
   ///    but with different opacities.
   static const Color white54 = Color(0x8AFFFFFF);
 
-  /// White with 30% opacity.
+  /// White with 38% opacity.
   ///
   /// Used for disabled radio buttons and the text of disabled flat buttons in dark themes.
   ///
@@ -363,7 +363,19 @@ class Colors {
   ///  * [ThemeData.disabledColor], which uses this color by default in dark themes.
   ///  * [Theme.of], which allows you to select colors from the current theme
   ///    rather than hard-coding colors in your build methods.
-  ///  * [white, white60, white54, white70, white12, white10], which are variants on this color
+  ///  * [white, white60, white54, white70, white30, white12, white10], which are variants on this color
+  ///    but with different opacities.
+  static const Color white38 = Color(0x62FFFFFF);
+
+  /// White with 30% opacity.
+  ///
+  /// ![](https://flutter.github.io/assets-for-api-docs/assets/material/Colors.whites.png)
+  ///
+  /// See also:
+  ///
+  ///  * [Theme.of], which allows you to select colors from the current theme
+  ///    rather than hard-coding colors in your build methods.
+  ///  * [white, white60, white54, white70, white38, white12, white10], which are variants on this color
   ///    but with different opacities.
   static const Color white30 = Color(0x4DFFFFFF);
 
@@ -375,7 +387,7 @@ class Colors {
   ///
   /// See also:
   ///
-  ///  * [white, white60, white54, white70, white30, white10], which are variants on this color
+  ///  * [white, white60, white54, white70, white38, white30, white10], which are variants on this color
   ///    but with different opacities.
   static const Color white24 = Color(0x3DFFFFFF);
 
@@ -387,7 +399,7 @@ class Colors {
   ///
   /// See also:
   ///
-  ///  * [white, white60, white54, white70, white30, white10], which are variants on this color
+  ///  * [white, white60, white54, white70, white38, white30, white10], which are variants on this color
   ///    but with different opacities.
   static const Color white12 = Color(0x1FFFFFFF);
 
@@ -397,7 +409,7 @@ class Colors {
   ///
   /// See also:
   ///
-  ///  * [white, white60, white54, white70, white30, white12], which are variants on this color
+  ///  * [white, white60, white54, white70, white38, white30, white12], which are variants on this color
   ///    but with different opacities.
   ///  * [transparent], a fully-transparent color, not far from this one.
   static const Color white10 = Color(0x1AFFFFFF);

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

@@ -505,7 +505,7 @@ class DataTable extends StatelessWidget {
           fontSize: 13.0,
           color: isLightTheme
             ? (placeholder ? Colors.black38 : Colors.black87)
-            : (placeholder ? Colors.white30 : Colors.white70),
+            : (placeholder ? Colors.white38 : Colors.white70),
         ),
         child: IconTheme.merge(
           data: IconThemeData(

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

@@ -81,7 +81,7 @@ class ExpandIcon extends StatefulWidget {
   ///
   /// Defaults to [Colors.black38] when the theme's
   /// [ThemeData.brightness] is [Brightness.light] and to
-  /// [Colors.white30] when it is [Brightness.dark]. This adheres to the
+  /// [Colors.white38] when it is [Brightness.dark]. This adheres to the
   /// Material Design specifications for [icons](https://material.io/design/iconography/system-icons.html#color)
   /// and for [dark theme](https://material.io/design/color/dark-theme.html#ui-application)
   final Color disabledColor;

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

@@ -62,7 +62,7 @@ final Color _kErrorDark = Colors.red.shade400;
 const Color _kCircleActiveLight = Colors.white;
 const Color _kCircleActiveDark = Colors.black87;
 const Color _kDisabledLight = Colors.black38;
-const Color _kDisabledDark = Colors.white30;
+const Color _kDisabledDark = Colors.white38;
 const double _kStepSize = 24.0;
 const double _kTriangleHeight = _kStepSize * 0.866025; // Triangle height. sqrt(3.0) / 2.0
 

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

@@ -249,7 +249,7 @@ class ThemeData extends Diagnosticable {
       splashColor: splashColor,
       materialTapTargetSize: materialTapTargetSize,
     );
-    disabledColor ??= isDark ? Colors.white30 : Colors.black38;
+    disabledColor ??= isDark ? Colors.white38 : Colors.black38;
     highlightColor ??= isDark ? _kDarkThemeHighlightColor : _kLightThemeHighlightColor;
     splashColor ??= isDark ? _kDarkThemeSplashColor : _kLightThemeSplashColor;
 

packages/flutter/test/material/expand_icon_test.dart

@@ -92,7 +92,7 @@ void main() {
     await tester.pumpAndSettle();
 
     iconTheme = tester.firstWidget(find.byType(IconTheme).last);
-    expect(iconTheme.data.color, equals(Colors.white30));
+    expect(iconTheme.data.color, equals(Colors.white38));
   });
 
   testWidgets('ExpandIcon test isExpanded does not trigger callback', (WidgetTester tester) async {