After a Qt5 update (5.12.1-1 -> 5.12.2-1) last night, KDE elements (tooltips, menus, ...) backgrounds color changed and rendered as light-gray. This makes content reading complicated.

Screenshots : https://pasteboard.co/I5OSXZku.png and https://pasteboard.co/I5OTbKGK.png

This happens after Qt5 update on my Lenovo Thinkpad E585 and HP Elitebook 850 G3.
I've try to change some theme configurations but no effects... Deactivate compositor seems to solve the problem but with bad effects on Latte Dock (and probably other components render).

KDE Plasma : 5.15.3-1
Theme color : Breeze dark
KDE Frameworks : 5.56.0
Kernel : 5.0.2-arch1-1-ARCH

Did you restart the machine or at least log out and back in after the upgrade?
You might also compare different desktop themes under System Settings -> Workspace Theme -> Desktop Theme to see if/how the problem manifests with different themes.

I think this bug is the same that :
- Reddit : https://www.reddit.com/r/kde/comments/b ... eeze_dark/
- Bug KDE : https://bugs.kde.org/show_bug.cgi?id=405548

Last plasma-framework package updates seems to solve the problem.