[Theming] Project Chroma - color palettes in Radiance

[kirill-grouchnikov]

This will track work to modernize the way Radiance defines color schemes, as well as some of the relevant painters.

More details will be added when 7.0 development starts, but in the meanwhile, some code pointers

1. SchemeBaseColors that defines the RGB colors that make up the "core" of the color scheme
2. SchemeDerivedColors that defines colors that are derived from the base colors and have specific usage. Material Design spec calls these system tokens, but I prefer to call them semantic colors
3. DerivedColorsResolverLight and DerivedColorsResolverDark that provide the default mapping of semantic colors to the underlying core scheme colors

Then, painters such as StandardFillPainter sometimes use the derived / semantic colors, and sometimes do an additional layer of "mixing" (like here) to get the colors they need for the visuals.

Recent additions in Radiance, such as fraction-based painters and direct values for derived / semantic colors made it easier for skins to have more precise control over the "flow" of RGB colors upwards into that skin's painters, the overall underlying system is showing the signs of its age.

The rough plan is to:

• Define a color scheme in terms of tonal stops (which is what most popular design systems today do), with "values" in the range between 0 and 100.
• Define semantic colors that map to the specific tonal stops in light and dark mode.
• Refactor existing painters to exclusively use semantic colors by default, with escape hatches to use direct mapping to the tonal stops.
• Refactor how light / dark color schemes are handled in Radiance. The idea is that a color scheme itself is not light or dark, but rather the skin is. And that defines what semantic color mappings that skin uses to the underlying tonal stops.

[kirill-grouchnikov]

Update: this is happening soon, and until this issue is closed, the main Radiance trunk will be unstable, undergoing major internal and API changes.

[kirill-grouchnikov]

Current (pre-Chroma) visuals of the Business Blue Steel skin:

New (Chroma) visuals of the Business Blue Steel skin:

[kirill-grouchnikov]

Current (pre-Chroma) visuals of the Business Black Steel skin:

New (Chroma) visuals of the Business Black Steel skin:

[kirill-grouchnikov]