This example demonstrates how you can set the PrintPreviewWindow theme to the currently selected GridControl theme. To do this, set the ThemeManager.ThemeName Attached Property in code:
[C#]ThemeManager.SetThemeName(preview,ThemeManager.GetThemeName(gridControl1));
Note that in this scenario, the GridControl should be printed via the VisualDataNodeLink like in the How to specify certain page settings programmatically when printing a grid example so that you can access the PrintPreviewWindow (preview variable in this example).