fixed custom asset colors serialization

.github/workflows/ci.yml

@@ -37,3 +37,6 @@ jobs:
 
       - name: Analyze root package
         run: flutter analyze
+
+      - name: Test root package
+        run: flutter test

lib/src/models/custom_assets/adaptyui_custom_assets_color.dart

@@ -1,7 +1,13 @@
 part of 'adaptyui_custom_assets.dart';
 
 extension on Color {
-  String get stringHexValue => '#${toARGB32().toRadixString(16).padLeft(8, '0').toUpperCase()}';
+  /// Converts Flutter's ARGB value to the RGBA wire format expected by AdaptyUI.
+  String get stringHexValue {
+    final argb = toARGB32();
+    final rgba = ((argb & 0x00FFFFFF) << 8) | ((argb >> 24) & 0xFF);
+
+    return '#${rgba.toRadixString(16).padLeft(8, '0').toUpperCase()}';
+  }
 }
 
 final class AdaptyCustomAssetColor extends AdaptyCustomAsset {

test/adapty_custom_asset_color_serialization_test.dart

@@ -0,0 +1,37 @@
+import 'package:adapty_flutter/adapty_flutter.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  group('AdaptyCustomAsset color serialization', () {
+    test('serializes solid colors as #RRGGBBAA', () {
+      final cases = <Color, String>{
+        const Color(0xFF0000FF): '#0000FFFF',
+        const Color(0x80010203): '#01020380',
+      };
+
+      for (final MapEntry(key: color, value: expected) in cases.entries) {
+        final asset = AdaptyCustomAsset.color(color: color);
+
+        expect(asset.jsonValue['value'], expected);
+      }
+    });
+
+    test('serializes linear gradient stop colors as #RRGGBBAA', () {
+      final asset = AdaptyCustomAsset.linearGradient(
+        gradient: const LinearGradient(
+          colors: [Color(0xFF0000FF), Color(0x80010203)],
+          stops: [0.25, 0.75],
+        ),
+      );
+
+      final values = asset.jsonValue['values'] as List<dynamic>;
+      final serializedColors = values
+          .cast<Map<String, dynamic>>()
+          .map((value) => value['color'])
+          .toList();
+
+      expect(serializedColors, ['#0000FFFF', '#01020380']);
+    });
+  });
+}