Since bug reports are often ignored for months or years, I thought to ask about this in a thread too; KF5 introduced the ability to change the titlebar color scheme per application via Window Rules. However, while this works with the default Breeze theme, it does not seem to apply to Aurorae themes with scheme-colored elements! Since Aurorae is the primary theme engine of KWin, this is definitely a strange problem to go unnoticed.

https://bugs.kde.org/show_bug.cgi?id=365994

Does anyone know why window rule colors don't apply to the titlebar and border with Aurorae themes that use color hints? Is this being worked on, when might it be fixed, and is a workaround? The themes I use and have tested with... both use the window / button colors for backgrounds and focus / hover colors for buttons:

https://www.kde-look.org/p/1002614/
https://www.kde-look.org/p/1002663/

Problem still present in Plasma 5.8.0.

Did anyone get to take a look at this so far? The problem does throw a wrench in some elements of system customization, as it makes the feature unusable with the theme I currently have.

Still a problem in Plasma 5.9.0. I would be happy if any of the developers could please offer more insight on this, and add the problem somewhere on their list.