Type Int1 does not conform to protocol BooleanType

[NOTE - See comment below. The .whiteColor and .blackColor methods were not actually being called as they should have been. The error message is still very bad though so I'm not resolving the issue.]

Compile error "Type 'Int1' does not conform to protocol 'BooleanType'" is occurring when I don't think it should. First encountered in application code but the below example has the same error in the Playground.

This isn't quite the minimal sample where this is happening but it is getting close. The error does disappear at some point in simplification even when I don't think that the types should fundamentally change.

class PLStandardTableViewCell {
    var title: UILabel? = nil
    
    func setSelected(selected: Bool) {
        title?.textColor = selected ? .whiteColor : .blackColor
    }
}