The DataGridView control uses the row template as a basis for all rows that it adds to the control either through data binding or when you call the System.Windows.Forms.DataGridViewRowCollection.Add method without specifying an existing row to use.
The row template gives you greater control over the appearance and behavior of rows than the RowsDefaultCellStyle property provides. With the row template, you can set any DataGridViewRow properties, including DefaultCellStyle.
3. DataGridView cell border color issue: Please take a look at the article below:
With the DataGridView control, you can customize the appearance of the control's border and gridlines to improve the user experience. You can modify the gridline color and the control border style in addition to the border styles for the cells within the control. You can also apply different cell border styles for ordinary cells, row header cells, and column header cells.