To change tab background in DXTabControl, use the BackgroundColor property. This property changes the tab background color when it's not active and affects the line color displayed in the tab header when it's active:
If you wish to customize header colors in different states (Selected, Focused, Hover, Normal), use the approach demonstrated at How To: Change the Tab Background in DXTabControl when a Tab is Selected, Focused, or Hovered.
To learn more about appearance customization in DXTabControl, refer to Appearance Customization.