QT apps are those that are made using the QT tool kit.
In case such apps like Clementine, qBittorrent, last.fm player use a different theme than the rest of your apps on Sabayon KDE, set them use the system's theme:
Alt+F2 -> qtconfig -> appearance -> GUI style -> Desktop settings (default)
Or you can, of course, choose any other style you like. The qtconfig tool is installed by default in your Sabayon KDE (if not, look it up through the packages and install).