[iOS 26] Switch with custom thumb color is losing color when coming back to app

Description

Using iOS 26, when you give a switch custom thumb colors, go to another app, come back to your app, then the custom colors are lost.

Steps to reproduce

1. Install the application on iOS 26.
2. Enable one of the toggles.
3. Switch app and come back.
4. Thumbs of switches which used to have a custom thumb color are white.

React Native Version

0.81.4

Affected Platforms

Runtime - iOS 26

Output of npx @react-native-community/cli info

System:
  OS: macOS 15.6.1
  CPU: (12) arm64 Apple M2 Pro
  Memory: 129.11 MB / 32.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 22.18.0
    path: ~/.nvm/versions/node/v22.18.0/bin/node
  Yarn:
    version: 4.6.0
    path: ~/.nvm/versions/node/v22.18.0/bin/yarn
  npm:
    version: 10.9.3
    path: ~/.nvm/versions/node/v22.18.0/bin/npm
  Watchman:
    version: 2025.09.15.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.15.2
    path: /Users/regina/.gem/ruby/3.2.2/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 25.0
      - iOS 26.0
      - macOS 26.0
      - tvOS 26.0
      - visionOS 26.0
      - watchOS 26.0
  Android SDK: Not Found
IDEs:
  Android Studio: 2024.3 AI-243.24978.46.2431.13363775
  Xcode:
    version: 26.0/17A324
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 17.0.13
    path: /usr/bin/javac
  Ruby:
    version: 3.2.2
    path: /Users/regina/.rubies/ruby-3.2.2/bin/ruby
npmPackages:
  "@react-native-community/cli":
    installed: 20.0.0
    wanted: 20.0.0
  react:
    installed: 19.1.0
    wanted: 19.1.0
  react-native:
    installed: 0.81.4
    wanted: 0.81.4
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: true
iOS:
  hermesEnabled: true
  newArchEnabled: true

Stacktrace or Logs

N/A

MANDATORY Reproducer

https://github.com/Regina-v/rn-ios26-switch-custom-color-bug

Screenshots and Videos

Screen record iOS 26: https://github.com/user-attachments/assets/33e01479-e9f7-4e29-9719-e9128a2ce1b9

Screen record iOS 18: https://github.com/user-attachments/assets/7b67f017-3ecd-46e7-accf-4b2773026c25

https://github.com/Regina-v/rn-ios26-switch-custom-color-bug の必須の再現用リポジトリから始め、レポートに示されているとおり、iOS 18 と比較しながら iOS 26 で switch の挙動を再現します。React Native の switch 実装を追跡し、アプリを離れて戻った後もカスタム thumb カラーが維持されることを確認します；報告された色の消失が発生しなくなれば完了です。