Hi, i found the issue.
It is another bug again 
, when MobileHDR is disabled in the Projects Settings, under Rendering, the camera image renders with wrong contrast. This happens on iOS, i have to android device to test, but it is the exact same problem.
Affected version are from UE4.22 to current UE4.24.
The fact that Unreal documentation tells users to disable MobileHDR(!) by setting graphics to “Scalable 2d/3d”
and that it takes over three full releases until this problem gets determined is a testament to Epics poor testing and no staff ever reading these forums or answerhub.
ARkit and ARCore plugins should to be marked as “experimental”, that would be honest, as they are too broken and undocumented.
If you test this on Android, please leave feedback if this solved it. I will submit a bug report and it would be helpful to mention whether both, ARKit on iOS and ARCore on Android, are affected in the same way.