I don't know if this is possible, but it would be great if Kwin could automatically adjust the titlebar/window frame color to an application's color scheme. Programs with dark KDE color schemes (such as Krita) look pretty awful with bright window borders. This can be fixed by adding windows rules for changing the window color scheme, but it would be better if Kwin could do that automatically. Reproducible: Always
This works by the application using KColorSchemeManager (see https://api.kde.org/frameworks/kconfigwidgets/html/classKColorSchemeManager.html ) which I added for this use case. In addition it needs a widget style which forwards a hint to KWin. This is implemented in breeze, but Krita (to my knowledge) hard disabled breeze. If it doesn't work with Krita, it's a bug in Krita either because they don't use KColorSchemeManager yet or because they hard disable breeze.
for not depending on the actual style: https://phabricator.kde.org/D3044
Alright. I'll open this as a bug for Krita then.