Hi Richard,
Thank you for your interest in Syncfusion products.
Please try setting below two properties to get the excel like fill down appearance.
this.gridControl1.AllowSelection = GridSelectionFlags.Cell;
this.gridControl1.AlphaBlendSelectionColor = Color.Black;
Here is the minimal sample which implements this task.
http://websamples.syncfusion.com/samples/grid.windows/F75891/main.htmPlease let me know if this helps.
Best Regards,
Srirajan.