FarPoint.Win.Spread.CellType.ButtonCellType btn = new
FarPoint.Win.Spread.CellType.ButtonCellType();
btn.BackgroundStyle = FarPoint.Win.BackStyle.Gradient;
btn.ButtonColor = Color.Yellow;
btn.ButtonColor2 = Color.Orange;
btn.GradientMode = Drawing2D.LinearGradientMode.ForwardDiagonal;
fpSpread1.ActiveSheet.Cells[0, 0].CellType = btn;