Block body background
The block body background, IIUC, is currently
fzjblue!10!white. This goes against the CD which in the section "Die Farben" says that primary and secondary colors are not to be displayed in halftones ("dürfen nicht aufgerastert werden").
For my course material, I use a different mechanism for creating boxes and have chosen
fzjgray as the box body background. Maybe this could work for the
beamer boxes as well?