Hello,
I have just upgraded to Fedora 26 from Fedora 24. I don't know much about KDE- although I prefer to use it- but I can tell you that my workstation has package plasma-workspace-5.10.5-2.fc26.x86_64. I hope that helps determine how up-to-date I am with KDE. Let me know if you need the versions of other things.

In any event, I have noticed that when I go to my Power / Session menu and choose, say, "reboot", there appears a screen overlay with choices ("Suspend", "Reboot", "Shutdown") and buttons "OK" and "Cancel".

In the past, this screen was a light grey haze, which meant the writing was easy to read. Now it's dark, and the lettering is dark, so I have a hard time making my choice.

I thought I'd point that out. Thanks.

Me too. Frustrating. Thanks for raising it.