Hi Ayden
Thank you for contacting Syncfusion Support.
In our ThemeStudio, you have option to export any theme project for particular control. In your exported project, you can get the theme file for particular control and also you can find some of the commonly maintained themes files in Common folder. In this common folder, you can find the brushes.xaml and common.xaml files, which contain the information regarding the brushes and repositories that has been used commonly for all controls. With this file, you can able to customize the control template of Ribbon control.
Please try this suggestion and let us know if it is helpful.
Regards,
Vijayalakshmi VR