anchor.diff:         assert(onError != null),
          assert(brightness != null);
   
  +  /// Create a ColorScheme based on a purple primary color that matches the
  +  /// [baseline Material color scheme](https://material.io/design/color/the-color-system.html#color-theme-creation).
     const ColorScheme.light({
       this.primary = const Color(0xff6200ee),
       this.primaryVariant = const Color(0xff3700b3),
  
positive.code:        assert(onError != null),
         assert(brightness != null);
  
    factory ColorScheme.fromSwatch({
      MaterialColor primarySwatch = Colors.blue,
      Color primaryColorDark,
  
negative.code: /// with [ColorScheme.fromSwatch].
  @immutable
  class ColorScheme extends Diagnosticable {
    /// Create a ColorScheme instance.
    const ColorScheme({
      @required this.primary,
      @required this.primaryVariant,
  