Hello witepo,

If I understand well your scenario, you are using AppStyle into your application. If so, to modify the group box area you could use one of these options:

Option 1: You could open your AppStyle and modify it. You could set BackColor or Background Image or Resourses. I made short video tutorial for you. Please take a look at attachments

Option 2: By default AppStyle has priority over Appearance properties, so you could set UseAppStyling property to False and apply your custom settings through properties in ultraGrid1.DisplayLayout.GroupByBox.Appearance

Option 3: You could use DrawFilter to set desired appearance or you could modify your AppStyle and set ResolutionOrder

Let me know if you have any questions.

Regards