well. in kcontrol > Appearance & Themes > GTK Styles and Fonts it's possible to employ different themes for GTK2 and GTK3 applications, and this fixes the menu color problem.
What I haven't been able to fix is the tiny fonts problem in TDE applications. Additionally, my cursor, in all its variants, has become *huge.*
Very strange indeed. And it came about from first unchecking and then rechecking Appearance & Themes > Colors > Apply colors to non-TDE applications.
How can this be?