flex_seed_scheme 1.3.0

A more flexible and powerful version of Flutter's ColorScheme.fromSeed. Use multiple seed colors, custom chroma and tone mapping.

FlexSeedScheme

A more flexible version of Flutter's ColorScheme.fromSeed.

Use this package like ColorScheme.fromSeed with the following additional capabilities:

• Use separate key colors to generate seed based tonal palettes for primary and optionally secondary, tertiary as well as error, neutral and neutral variant colors in ColorScheme.
• Change the chroma limits and values used in the Material 3 default strategy for tonal palette generation in the new Google HCT (Hue-Chroma-Tone) color space.
• Change which tones in the generated core tonal palettes are used by which ColorScheme color. Changes are limited to the tones from correct core palette for each ColorScheme color, but any tone from it can be used. Going up or down one tone is often usable, in some cases even two.
• Use two additional tonal palettes tones, 5 and tone 98. They can be used to offer more fidelity at the dark and light end of the tonal palettes, and can be mapped to ColorScheme colors when using custom tone mapping. Tone 98 was previously also available in the web-based Material 3 Theme Builder, but is no longer so, and is also not included in the Material 3 design guide. The guide explicitly mentions thirteen tones and excludes tone 98. With FlexSeedScheme you can use fifteen tones, including 98 and 5.

Background

This package was extracted from the customizable color scheme seeding engine in the FlexColorScheme package to its own package.

This allows developers to use the same customizable ColorScheme seeding algorithms used by FlexColorScheme, without using the FlexColorScheme package. Starting with FlexColorScheme version 6 and later, it depends on this package instead.

If you use FlexColorScheme version 6 or later, you do not need to add FlexSeedScheme to use its features, FlexColorScheme exports its API as well. If you use FlexColorScheme you typically do not even need to use FlexSeedScheme directly, its usage is baked in and used based on how you configure FlexColorScheme.

Getting Started

Add the flex_seed_scheme package to pubspec.yaml:

dart pub add flex_seed_scheme or flutter pub add flex_seed_scheme

Usage

Import the package to use it:

import 'package:flex_seed_scheme/flex_seed_scheme.dart';

Define seed key colors that will be used to compute your seed generated ColorScheme.

// Define your seed colors.
const Color primarySeedColor = Color(0xFF6750A4);
const Color secondarySeedColor = Color(0xFF3871BB);
const Color tertiarySeedColor = Color(0xFF6CA450);

With FlexSeedScheme you make a seed generated ColorScheme using SeedColorScheme.fromSeeds. It works like ColorScheme.fromSeed, but instead of only accepting a single seed color, it can use six key colors as seed colors. One for each main color (primary, secondary and tertiary) group in ColorScheme. You can customize the error colors, typically there is no need to do so, but if your primary color is of a red hue, that conflicts with the error colors, then adjusting the error color is a possibility. You can also use custom key colors to seed generate the neutral and neutral variant palettes, that are used to define all the surface and background colors in ColorScheme. We recommend sticking to the default that uses primary key color's hue with very low chroma.

Chroma limits that differ from Material 3 defaults for tonal palette generation, can also be defined. Additionally, tone mapping, that defines which tone is used by what ColorScheme color, can be customized. Both are done via FlexTones passed in to tones.

Typically, you should use the same key colors and tones setup to produce the ColorScheme for light and dark theme mode. This guarantees that the light and dark theme use identical generated tonal palettes, and only vary based on which tones are used for what color in light and dark mode. This results in matching light and dark theme colors. This is just the norm though, feel free to experiment.

    // Make a light ColorScheme from the seeds.
    final ColorScheme schemeLight = SeedColorScheme.fromSeeds(
      brightness: Brightness.light,
      // Primary key color is required, like seed color ColorScheme.fromSeed.
      primaryKey: primarySeedColor,
      // You can add optional own seeds for secondary and tertiary key colors.
      secondaryKey: secondarySeedColor,
      tertiaryKey: tertiarySeedColor,
      // Tone chroma config and tone mapping is optional, if you do not add it
      // you get the config matching Flutter's Material 3 ColorScheme.fromSeed.
      tones: FlexTones.vivid(Brightness.light),
    );

    // Make a dark ColorScheme from the seeds.
    final ColorScheme schemeDark = SeedColorScheme.fromSeeds(
      brightness: Brightness.dark,
      primaryKey: primarySeedColor,
      secondaryKey: secondarySeedColor,
      tertiaryKey: tertiarySeedColor,
      tones: FlexTones.vivid(Brightness.dark),
    );

You can use separate key colors as seeds to generate the primary, secondary and tertiary tonal palettes. If no key color for secondaryKey and/or tertiaryKey are provided, they use primaryKey color as their seed color value.

If you only specify primaryKey color as seed, and no custom tones configuration, identical ColorScheme result to ColorScheme.fromSeed is produced.

The default chroma limits in the HCT color space used for seed generated colors for secondary and tertiary colors in ColorScheme.fromSeed have quite low chroma values. This makes the colors fairly muted or pastel like. This is especially the case with secondary colors. This is by design in the standard Material 3 color palette. You can tune this behavior by passing in a custom FlexTones configuration to tones. There are pre-made configurations you can use, above FlexTones.vivid was used. It is also easy to make custom configurations. Look in FlexTones and use the pre-made definitions as inspiration for your own configs.

Using the above configuration, the following core palettes are generated, in order from top to bottom:

• Primary tonal palette
• Secondary tonal palette
• Tertiary tonal palette
• Error tonal palette
• Neutral tonal palette
• Neutral variant tonal palette

The above color tones in the above palettes are then mapped to ColorScheme colors. Mapping is different for light and dark theme mode in order to create a color scheme with suitable contrast. With the example FlexTones.vivid setup used in tones, the light ColorScheme is mapped as shown below:

And the dark ColorScheme becomes:

We can, for example, see that in light mode, the primary tone 30, is assigned to ColorScheme.primary color and tone 90 to primaryContainer. In dark mode they get tones 80 and 20. Similar assignments are repeated for secondary, tertiary, error colors and all the surface and background colors. It is this mapping that FlexTones gives you control over.

Define ThemeData

In your MaterialApp you then define your light and dark mode themes using the seed generated ColorSchemes just as you would with any other ColorScheme. For example:

  @override
    Widget build(BuildContext context) {
      return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'SeedColorScheme.fromSeeds Demo',
      themeMode: ThemeMode.system,  
      theme: ThemeData.from(
        colorScheme: schemeLight,
        useMaterial3: true,
      ),
      darkTheme: ThemeData.from(
        colorScheme: schemeDark,
        useMaterial3: true,
      ),
      home: HomePage(),
    );
  }

Override Color Values

All colors in the seed produced ColorScheme can be overridden by providing each ColorScheme color property in SeedColorScheme.fromSeeds a given color value. This feature is equivalent to ColorScheme.fromSeed.

This is typically used to assign a given color value to primary color, which is often used as app brand color. When the brand color is used as primaryKey seed color, it typically does not end up as the primary color in the seed generated ColorScheme. Having a given brand color as primary color is often desired. To get the seed color as your primary brand color, assign the color used as primaryKey to primary color as well.

    // Make a light ColorScheme from the seeds.
    final ColorScheme schemeLight = SeedColorScheme.fromSeeds(
      brightness: Brightness.light,
      // Use a "brand" seed color as primary color in the result.
      primary: primarySeedColor,
      primaryKey: primarySeedColor,
      //
      secondaryKey: secondarySeedColor,
      tertiaryKey: tertiarySeedColor,
      tones: FlexTones.vivid(Brightness.light),
    );

This strategy works well for the light mode ColorScheme, since the prominent brand color a company has defined is typically intended to be printed on white paper. If you have secondary brand colors that are to be used, using them as seeds for secondaryKey and tertiaryKey will work too. How well they will fit and match the Material 3 color system, if assigned to secondary and tertiary directly as colors in SeedColorScheme.fromSeeds, will vary depending on what colors they are.

Companies rarely have brand colors suited for good contrast in dark theme mode. In that case prefer only using the same light mode brand colors as key colors to seed the dark mode ColorScheme. If they do have dark mode specifications, and the colors are of same hue as light mode, consider still using the light mode colors as the seed source, and only applying the appropriate dark mode colors to primary, secondary and tertiary as needed.

If there is a spec that calls for completely different main colors in dark mode, with different hues, then seeding from them and also setting primary, secondary and tertiary to these color values is appropriate.

Customize Tones and Chroma

In the above example, we used a predefined tone mapping and chroma setup called FlexTones.vivid. There are currently nine predefined configurations available:

• FlexTones.material, default and same as Flutter SDK M3 setup.
• FlexTones.soft, softer and earthier tones than M3 FlexTones.material.
• FlexTones.vivid, more vivid colors, uses chroma as defined by each given key color.
• FlexTones.vividSurfaces, like vivid, but with more color tint in surfaces and backgrounds.
• FlexTones.highContrast, can be used for more color-accessible themes.
• FlexTones.ultraContrast, for a very high-contrast theme version.
• FlexTones.jolly, for a more "jolly" and colorful theme.
• FlexTones.vividBackground, like vividSurfaces, but tone mapping for surface and background are swapped.
• FlexTones.oneHue, a balanced chromatic setup. It is called oneHue because When only primary color is used as seed, it does not rotate its hue value to make a computed hue for tertiary tonal palettes, but uses the same hue. This makes it possible to make seed-generated color schemes from a single color. In such themes, all colors are based on the same hue, but using different chroma and tones to create a one color hue based theme.

You can define custom tones mapping and chroma limitation setups with FlexTones. Prefer using the FlexTones.light and FlexTones.dark constructors as base for custom definitions. By using them, you only need to override defaults that you want to change.

// Example definition of light custom tones config.
const FlexTones myLightTones = FlexTones.light(
  primaryTone: 30, // Default is 40.
  onPrimaryTone: 95, // Default is 100
  onSecondaryTone: 95, // Default is 100
  onTertiaryTone: 95, // Default is 100
  onErrorTone: 95, // Default is 100
  primaryMinChroma: 55, // Default is 48
  secondaryChroma: 25, // Default is 16
  tertiaryChroma: 40, // Default is 24
  neutralChroma: 7, // Default is 4,
  neutralVariantChroma: 14, // Default is 8
);

// Example definition of dark custom tones config.
const FlexTones myDarkTones = FlexTones.dark(
  primaryTone: 70, // Default is 80.
  onPrimaryTone: 10, // Default is 20
  onSecondaryTone: 10, // Default is 20
  onTertiaryTone: 10, // Default is 20
  onErrorTone: 10, // Default is 20
  primaryMinChroma: 55, // Default is 48
  secondaryChroma: 25, // Default is 16
  tertiaryChroma: 40, // Default is 24
  neutralChroma: 7, // Default is 4,
  neutralVariantChroma: 14, // Default is 8
);

Accessibility

You can use FlexTones to create a seed generated ColorScheme, that is based on same colors as your standard theme's light and dark scheme colors, but uses a chroma configuration and tone mapping setup that increases contrast further from standard light and dark theme setup.

There are two high contrast FlexTones configuration pre-made for this. They are called FlexTones.highContrast, a colorful high-contrast version, and FlexTones.ultraContrast, a less colorful version, a more dark on light in light theme mode, and light on dark in dark mode.

// Make a high contrast light ColorScheme from the seeds.
final ColorScheme schemeLightHc = SeedColorScheme.fromSeeds(
  brightness: Brightness.light,
  primaryKey: primarySeedColor,
  secondaryKey: secondarySeedColor,
  tertiaryKey: tertiarySeedColor,
tones: FlexTones.highContrast(Brightness.light),
);

// Make a ultra contrast dark ColorScheme from the seeds.
final ColorScheme schemeDarkHc = SeedColorScheme.fromSeeds(
  brightness: Brightness.dark,
  primaryKey: primarySeedColor,
  secondaryKey: secondarySeedColor,
  tertiaryKey: tertiarySeedColor,
  tones: FlexTones.ultraContrast(Brightness.dark),
);

If you then define equivalent ThemeData based on those schemes as your standard MaterialApp, theme and darkTheme definitions, but assign them to highContrastTheme and highContrastDarkTheme, you get more accessible themed colors that are based on same colors, but with higher contrast, that are activated when users select high-contrast theme in device accessibility system settings. Changing to accessibility theme based on device system setting automatically, by using theme data defined on MaterialApp properties highContrastTheme and highContrastDarkTheme, is only supported on iOS devices in the current version of Flutter SDK.

      // Define accessibility high contrast versions using same color base.
      //
      highContrastTheme: ThemeData.from(
        colorScheme: schemeLightHc,
        useMaterial3: true,
      ),
      highContrastDarkTheme: ThemeData.from(
        colorScheme: schemeDarkHc,
        useMaterial3: true,
      ),

Another way to modify FlexTones configurations for contrast and accessibility, is by forcing all main onColors and all surface onColors to only use black and white contrasting colors. If we remove in the Material 3 guide used color system's colored contrasting colors, we can improve color accessibility and contrast on any FlexTones configuration. We can do this with the FlexTones modifying methods onMainsUseBW(), for main onColors and with onSurfacesUseBW() for the surface onColors. The main colors are primary, secondary, tertiary, error and their containers. The surface colors are background, surface, surfaceVariant and inverseSurface.

// Make a Material 3 seeded light ColorScheme, 
// but with always black and white contrasting onColors.
final ColorScheme schemeLightOnBW = SeedColorScheme.fromSeeds(
  brightness: Brightness.light,
  primaryKey: primarySeedColor,
  secondaryKey: secondarySeedColor,
  tertiaryKey: tertiarySeedColor,
tones: FlexTones.material(Brightness.light).onMainsUseBW().onSurfacesUseBW(),
);

// Make a Vivid dark ColorScheme, 
// but with always black and white contrasting onColors.
final ColorScheme schemeDarkOnBW = SeedColorScheme.fromSeeds(
  brightness: Brightness.dark,
  primaryKey: primarySeedColor,
  secondaryKey: secondarySeedColor,
  tertiaryKey: tertiarySeedColor,
  tones: FlexTones.vivid(Brightness.dark).onMainsUseBW().onSurfacesUseBW(),
);

Example Application

The included example application uses above color seeding and custom tone mapping, and you can also choose any of the built-in pre-configured tone mappings. You can choose to use secondary and primary seed colors as additional keys to generate the color schemes. You can also try to keep all the contrasting onColors black and white.

With the app we can compare results from FlexSeedScheme.fromSeeds, to using the single seed color ColorScheme.fromSeed seed generated Material 3 ColorScheme available in Flutter.

Both use the same key color as primary seed color, but ColorScheme.fromSeed can only use it as a single seed color, we cannot get any hues from our primary and secondary key colors in the produced seed generated ColorScheme with it.

With ColorScheme.fromSeed we can also not customize the colorfulness (chroma) of its seed generated secondary and tertiary colors. Like we can with FlexSeedScheme.fromSeeds, demonstrated here by choosing different FlexTones configurations. The tonal palette tones to ColorScheme color mappings can also not be modified, lie we can do with FlexSeedScheme.fromSeeds.

Light from seeds - Custom tones	Dark from seeds - Custom tones

Light from single seed - Material 3 tones	Dark from single seed - Material 3 tones

You can try a web version of this example here.