Hello Shaolin,

If you need to set the appearance of all the cells in grid’s filter row, you may set FilterCellAppearance or FilterRowAppearance of the Override like this:

var layout = this.ultraGrid1.DisplayLayout;
var ov = layout.Override;
 
ov.FilterCellAppearance.BackColor = Color.Blue;
ov.FilterRowAppearance.BackColor = Color.Green;

If what you need is to set the appearance of a single cell in filter row you will need to use some workaround, as grid does not expose method or property allowing you to achieve this. One possible solution is to handle BeforeEnterEditMode and AfterExitEditMode evnets of the grid. In before event check if the edited cell is filter row cell. If so, set the necessary appearance. In after event check again the cell if it is filter row cell – if so reset its appearance. You can use code like this:

private void UltraGrid1_BeforeEnterEditMode(object sender, CancelEventArgs e)
{
    //  Get a reference to the grid
    var grid = sender as UltraGrid;
    if(grid == null)
        return;
 
    //  Get a reference to the active cell
    var activeCell = grid.ActiveCell;
    if(activeCell == null)
        return;
 
    //  If active cell is filter row cell set its appearance
    if(activeCell.IsFilterRowCell == true)
    {
        //  As each time user clicks on filter row cell you will set cell's appearance
        //  it is better to cache the appearance in a private field. This way you will
        //  decrease the memory footprint
        if(this.editApp == null)
        {
            //  Initialize edit appearance if not yet done
            this.editApp = new Infragistics.Win.Appearance();
            this.editApp.BackColor = Color.Red;
        }
 
        if(this.defaultApp == null)
        {
            //  Save current cell appearance
            this.defaultApp = new Infragistics.Win.Appearance();
            this.defaultApp = (Infragistics.Win.Appearance)activeCell.Appearance.Clone(); 
        }
 
        //  Set cell appearance
        activeCell.Appearance = this.editApp;
    }
}
 
private void UltraGrid1_AfterExitEditMode(object sender, EventArgs e)
{
    //  Get a reference to the grid
    var grid = sender as UltraGrid;
    if(grid == null)
        return;
 
    //  Get a reference to the active cell
    var activeCell = grid.ActiveCell;
    if(activeCell == null)
        return;
 
    //  If the cell is filter row cell restore its default appearance
    if(activeCell.IsFilterRowCell == true && this.defaultApp != null)
        activeCell.Appearance = this.defaultApp;
}

Attached is a small sample where I have implemented this approach. Please check my sample and let me know if this is what you are looking for or if I am missing something.