To reproduce the problem case1:
 - Set dark mode in macOS
 - Set Highlight color to "Graphite"
 - Run the SwingSet2
 - Open the source code of any demo
 - Press cmd+A to select the whole text
 - Text selection will not be visible
 - Move the focus out/in of the text component, selection becomes visible

To reproduce the problem case2:
 - Set dark mode in macOS
 - Set Highlight color to "Graphite"
 - Run the SwingSet2
 - Open JInternalDemo
 - Try to select "Frame" text in the internal frame
 - The text itself and selection will disappear(we will draw white on white?)

The bug can be reproduced on macOS 10.15 Beta 9 (19A573a), I do not know when it was introduced.

The Aqua L&F is affected only.