Mac Catalyst - can't override highlight color in UITextField

I want to override the highlight color for text in UITextFields (for a Mac Catalyst app) so that I can't actually see it. I've tried setting the tintColor property to UIColor.clear, but it has no effect: when I select text, behind it I see the color that the user selects in System Preferences >> General >> Highlight color.

Here is a picture of the problem: hi.stack.imgur.com/ku2iJ.png

The text is highlighted, but instead of yellow (the background color of the UITextField), it's showing the highlight color (blended with the yellow).

Is this a bug? What's the work around? Any hints would be greatly appreciated!