I have a problem with transparency in my Views, especially with
tableView.backgroundColor = UIColor.clear
Found the problem: When instantiating a variable which holds the view before displaying it, the background color of this view is white. The debugger calls this UICachedDeviceWhiteColor.
Why would you do that? If you instantiate the view before it is displayed, you can switch with a menu between different views very fast with "bringSubview(toFront: ...).
How to fix: To fix this you have to instantiate the view every time you want to show it.
Hope I could help some lost souls with this answer and Apple is going to fix this bug.