Steps to reproduce:

1) Open Unity Hub and create a new project
2) Switch platform to iOS
3) Leave Metal as the only Graphics API in the Player Settings
4) Add DisplayP3 Color Gamut in the Player Settings
5) Build this project and open in xCode
6) Make a build and launch on iPhone XS
Observe: Metal errors in the Console:

Filename: ./Runtime/Graphics/Texture2D.cpp Line: 776)
Invalid texture format (0) for Texture2D
(Filename: ./Runtime/Graphics/Texture2D.cpp Line: 582)
asdfasdfxczDisplaP3 was compiled with optimization - stepping may behave oddly; variables may not be available.
(lldb)

Reproduced with:
2019.1.0b9

Device under testing:
VLNQA0212 iPhone Xs

----------------------------
Fixed in:
2019.2.0b2