alpha ignored in modern rgb() syntax

[wojtekmaj]

Description

rgb() syntax appears to be only parsing R, G, and B channels, ignoring A, despite specs allowing it and all web browsers respecting it.

Steps to reproduce

1. Use rgb(R G B / A) color anywhere in the code
2. You get black instead

React Native Version

0.78.1

Affected Platforms

Runtime - iOS

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

System:
  OS: macOS 15.3.1
  CPU: (8) arm64 Apple M2
  Memory: 221.89 MB / 16.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 22.14.0
    path: /private/var/folders/3y/swkjq1x101b76mzjgt4pm2d80000gp/T/xfs-39046bc3/node
  Yarn:
    version: 4.3.1
    path: /private/var/folders/3y/swkjq1x101b76mzjgt4pm2d80000gp/T/xfs-39046bc3/yarn
  npm:
    version: 10.9.2
    path: /usr/local/bin/npm
  Watchman: Not Found
Managers:
  CocoaPods:
    version: 1.16.2
    path: /opt/homebrew/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 24.2
      - iOS 18.2
      - macOS 15.2
      - tvOS 18.2
      - visionOS 2.2
      - watchOS 11.2
  Android SDK: Not Found
IDEs:
  Android Studio: Not Found
  Xcode:
    version: 16.2/16C5032a
    path: /usr/bin/xcodebuild
Languages:
  Java: Not Found
  Ruby:
    version: 2.6.10
    path: /usr/bin/ruby
npmPackages:
  "@react-native-community/cli":
    installed: 15.0.1
    wanted: 15.0.1
  react:
    installed: 18.3.1
    wanted: 18.3.1
  react-native:
    installed: 0.76.6
    wanted: 0.76.6
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: true
iOS:
  hermesEnabled: true
  newArchEnabled: false

Stacktrace or Logs

not applicable

Reproducer

https://snack.expo.dev/u9FC-9ROpkNTvjfeWs6C6

Screenshots and Videos

Source: https://snack.expo.dev/u9FC-9ROpkNTvjfeWs6C6

Trying the exact same code on the web (minimally edited for obvious reasons) works:

Source: https://codesandbox.io/p/devbox/distracted-pond-k68g7k / https://k68g7k.csb.app/

[react-native-bot]

Tip

Newer version available: You are on a supported minor version, but it looks like there's a newer patch available - 0.78.1. Please upgrade to the highest patch for your minor or latest and verify if the issue persists (alternatively, create a new project and repro the issue in it). If it does not repro, please let us know so we can close out this issue. This helps us ensure we are looking at issues that still exist in the most recent releases.

[react-native-bot]

Tip

Newer version available: You are on a supported minor version, but it looks like there's a newer patch available - undefined. Please upgrade to the highest patch for your minor or latest and verify if the issue persists (alternatively, create a new project and repro the issue in it). If it does not repro, please let us know so we can close out this issue. This helps us ensure we are looking at issues that still exist in the most recent releases.

[NickGerleman]

ViewConfig processor based color parsing have a good number of bugs and missing features. This one and some others will be fixed sometime in the future when we roll out new native parser (see https://github.com/facebook/react-native/blob/main/packages/react-native/ReactCommon/react/renderer/css/CSSColorFunction.h)