I've always enjoyed great GTK theme integration with GTK 2 apps using the oxygen GTK theme (under gnome application style in system settings). Recently Chrome and Firefox have apparently started using GTK 3. Neither the breeze-gtk nor Breeze-dark-gtk follow my system colors. I need a GTK 3 theme that honors my system colors. Where can I find a GTK 3 theme that follows my KDE system colors? (I do have the "Apply colors to non-QT applications" checked in the color scheme of system settings)

You can try downloading and installing the "named-colors" branch of gnome-breeze: https://github.com/dirruk1/gnome-breeze ... med-colors. Note, as I understand it, that this branch is unmaintained and wasn't copied over when the project was imported into KDE's main git repo (see https://github.com/KDE/breeze-gtk).

I'm certainly with you on this one. I'm always using "non-standard" color schemes and want the themes of my gtk apps to match (and I don't want have to hand-edit the gtk and qt themes just to change the colors).

Modifying a GTK theme by hand was too daunting and I couldn't get the above suggested theme to work. But I found a solution that worked well for me. I found that there's a GTK3 theme with a color modifying GUI. By downloading the Numix theme and setting it as the GTK3 theme in system settings/application style/GNOME application style I could then run the program Oomox I found on github. The Oomox program has a GUI that let me set most of the window and button elements of the Numix theme. Now my Firefox and Chrome match very well with the rest of my system.