feat: Expose brighten and darken helpers on palette

doc/flame/rendering/palette.md

@@ -86,3 +86,6 @@ members:
 - `paint`: creates a new `Paint` with the color specified. `Paint` is a non-`const` class, so this
   method actually creates a brand new instance every time it's called. It's safe to cascade
   mutations to this.
+
+It also exposes helper methods to derive a new `PaletteEntry` by transforming the underlying color,
+such as `withRed` or `lighten`.

packages/flame/lib/src/palette.dart

@@ -1,5 +1,7 @@
 import 'dart:ui';
 
+import 'package:flame/extensions.dart';
+
 class PaletteEntry {
   final Color color;
 
@@ -22,6 +24,14 @@ class PaletteEntry {
   PaletteEntry withBlue(int blue) {
     return PaletteEntry(color.withBlue(blue));
   }
+
+  PaletteEntry darken(double amount) {
+    return PaletteEntry(color.darken(amount));
+  }
+
+  PaletteEntry brighten(double amount) {
+    return PaletteEntry(color.brighten(amount));
+  }
 }
 
 class BasicPalette {

packages/flame/test/palette_test.dart

@@ -0,0 +1,22 @@
+import 'package:flame/palette.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('Palette', () {
+    test('updates color', () {
+      const entry = BasicPalette.red;
+      expect(entry.color, const Color(0xFFFF0000));
+      expect(entry.withAlpha(100).color, const Color(0x64FF0000));
+      expect(entry.withRed(100).color, const Color(0xFF640000));
+      expect(entry.withGreen(100).color, const Color(0xFFFF6400));
+      expect(entry.withBlue(100).color, const Color(0xFFFF0064));
+    });
+
+    test('darkens and brightens color', () {
+      const entry = BasicPalette.red;
+      expect(entry.color, const Color(0xFFFF0000));
+      expect(entry.darken(0.5).color, const Color(0xFF800000));
+      expect(entry.brighten(0.5).color, const Color(0xFFFF8080));
+    });
+  });
+}