Thank you for the project.
I've noticed that you use Xaml binaries and merge them in App.xaml. You should reference NoXAML DLLs when using implicit styles approach as described in our online documentation.
This way the background of RadComboBox
will get the correct color.
You could also use StyleManager but in this case you should remove merged dictionaries from App.xaml and apply StyleManager in code behind as follow:
Please let me know if this helps.
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