This seems to happen when users unlock their phone, or when Dark Mode and Night Shift are activated. However, if you’re wondering if this could be a hardware problem, that might not necessarily be the case. This is because users are reporting that this issue only happened following the update to iOS 13.5.
This suggests that this is a software problem, and it seems that the green tint does go away after a while, although it does come back every now and then, which we imagine can be rather annoying. There is no way to fix this bug so for now, iPhone users will just have to deal with it, but Apple is working on the iOS 13.5.5 update, so perhaps a fix could be in there.
For now, it also appears that this issue mostly affects iPhone 11 users, and that owners of Apple’s older iPhones are not affected.