private void Form1_Load(object sender, EventArgs e)
{
    HoverButtonCellType buttonCt = new HoverButtonCellType();
    fpSpread1.ActiveSheet.Cells[2, 2].CellType = buttonCt;

}
public class HoverButtonCellType : FarPoint.Win.Spread.CellType.ButtonCellType
{
    public override void PaintCell(Graphics g, Rectangle r, FarPoint.Win.Spread.Appearance appearance, object value, bool isSelected, bool isLocked, float zoomFactor)
    {
        if (appearance.MouseOver)
        {
            System.Windows.Forms.VisualStyles.VisualStyleElement element = System.Windows.Forms.VisualStyles.VisualStyleElement.Button.PushButton.Hot;
            if (System.Windows.Forms.VisualStyles.VisualStyleRenderer.IsElementDefined(element))
            {
                FarPoint.Win.FpVisualStyleRenderer vsr = new FarPoint.Win.FpVisualStyleRenderer(element);
                vsr.DrawBackground(g, r);
                return;
            }
        }

        base.PaintCell(g, r, appearance, value, isSelected, isLocked, zoomFactor);
    }
}