Adds wide gamut framework breakage notice.

src/release/breaking-changes/wide-gamut-framework.md

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+---
+title: Migration guide for wide gamut Color
+description: Description on Color changes for wide gamut support and migration
+             instructions.
+---
+
+## Summary
+
+The API for the [`Color`][] class in `dart:ui` is changing to support wide gamut
+colors.
+
+## Context
+
+Wide gamut color support was [added to the renderer][] previously. That support
+is now being plumbed up [to the Flutter Framework][] so those colors can be used
+by UIs.
+
+## Description of change
+
+Changes to [`Color`][]:
+
+ 1. Adds a enum field which will specify its [`ColorSpace`][].
+ 1. Adds API to use normalized floating-point color components.
+ 1. Removes API that uses 8-bit unsigned integer color components that can lead
+    to data loss.
+
+Changes to [`ColorSpace`][]:
+
+ 1. `displayP3` will be added.
+
+## Migration guide
+
+### 8-bit unsigned integer constructors
+
+Constructors like `Color.fromARGB` will remain unchanged and have continued
+support. If one wants to take advantage of Display P3 colors they will have to
+use the new `Color.from` constructor that takes normalized floating-point
+color components.
+
+### Implementors of `Color`
+
+There are new methods being added to `Color` so any class that `implements`
+Color will break and have to implement the new methods like `Color.a`, and
+`Color.b`. Ultimately implementors should be migrated to take advantage of the
+new API. In the short-term, these methods can easily be implemented without
+changing the underlying structure of your class.
+
+For example:
+
+```dart
+class Foo implements Color {
+  int _red;
+
+  @override
+  double get r => _red * 255.0;
+}
+```
+
+### Color space support
+
+Clients that use `Color` and perform any sort of calculation on the color
+components should now be checking the color space component before doing any
+such calculation. `Color` has a new method `Color.withValues` that can be used
+to perform color space conversions to help with that.
+
+For example:
+
+```dart
+// Before
+double redRatio(Color x, Color y) => x.red / y.red;
+
+// After
+double redRatio(Color x, Color y) {
+  final xPrime = x.withValues(colorSpace: ColorSpace.extendedSRGB);
+  final yPrime = y.withValues(colorSpace: ColorSpace.extendedSRGB);
+  return xPrime.r / yPrime.r;
+}
+```
+
+### Color component accessors
+
+For users of `Color`, if the components are ever accessed the code should be
+migrated to take advantage of the floating-point components. In the short term
+one can easily scale the components themselves.
+
+```dart
+extension IntColorComponents on Color {
+  int get intAlpha => this.a ~/ 255;
+  int get intRed => this.r ~/ 255;
+  int get intGreen => this.g ~/ 255;
+  int get intBlue => this.b ~/ 255;
+}
+```
+
+## Timeline
+
+### Phase 1 - New API introduction, old API deprecation
+
+**Release to stable:** TBD
+**PR:**: [PR 54737][]
+
+### Phase 2 - Old API removal
+
+**Release to stable:** TBD
+
+## References
+
+Relevant PRs:
+
+* [issue 127855][]: Implement wide gamut color support in the Framework
+
+[`Color`]: {{site.api}}/flutter/dart-ui/Color-class.html
+[added to the renderer]: {{site.repo.flutter}}/issues/55092
+[to the Flutter Framework]: {{site.repo.flutter}}/issues/127855
+[issue 127855]: {{site.repo.flutter}}/issues/127855
+[`ColorSpace`]: {{site.api}}/flutter/dart-ui/ColorSpace.html
+[PR 54737]: {{site.repo.engine}}/pull/54737