To reproduce:

1. Download attached "ReadPixelsTest.zip" project and open in Unity
2. Open "SampleScene" scene
3. Change Color Gamut to DisplayP3
4. Build for iOS
5. Deploy the Xcode project to the iOS device
6. Press "READ PIXELS" button
7. Observe that ReadPixels returns Texture with Pink colors

Notes:
- This issue does not reproduce on Windows Editor and Standalone, macOS Editor and Standalone, and Android
- This issue happens only on iOS Devices which supports DisplayP3 Native Color Space
- If You change Color Gamut to sRGB, it returns Correct Colors
- Images for reference are shared in Comments section

Tested with:
- iPhone XS, iOS: 12.0 - Reproduced
- iPhone 8 Plus, iOS: 12.2 - Reproduced
- Google Pixel 2 - Not Reproduced
- iPhone 6 Plus, iOS: 12.1.4 - Not Reproduced

Reproduced on Unity 2017.4.0f1, 2017.4.26f1, 2018.3.14f1, 2018.4.0f1, 2019.1.2f1, 2019.2.0a14 and 2019.3.0a3