is it possible to change the opacity of the RadRibbonView GroupHeader? We want to increase the readability of the group header and we can't find any sources on how to increase the opacity.
To change the appearance of the group headers, you will need to extract the template of the GroupChrome element and adjust the properties (Opacity/FontWeight) of the ContentControl responsible for displaying the header.
For your convenience, I've prepared a small sample project where I've done this for the Office2016 theme. If you're using another theme, however, you'd need to extract and modify its template accordingly.