PdfShading shading = PdfShading.SimpleAxial(pdfWriter, x0, y0, x1, y1, BaseColor.YELLOW, BaseColor.RED);
PdfShadingPattern pattern = new PdfShadingPattern(shading);
ShadingColor color = new ShadingColor(pattern);

using System.Diagnostics;
using System.IO;
using iTextSharp.text;
using iTextSharp.text.pdf;

namespace iTextSharpGradientTest
{
    public class GradientCellEvent : IPdfPCellEvent
    {
        public void CellLayout(PdfPCell cell, Rectangle position, PdfContentByte[] canvases)
        {
            var cb = canvases[PdfPTable.BACKGROUNDCANVAS];
            cb.SaveState();

            var shading = PdfShading.SimpleAxial(
                                    cb.PdfWriter,
                                    position.Left, position.Top, position.Left, position.Bottom,
                                    BaseColor.YELLOW, BaseColor.ORANGE);
            var shadingPattern = new PdfShadingPattern(shading);

            cb.SetShadingFill(shadingPattern);
            cb.Rectangle(position.Left, position.Bottom, position.Width, position.Height);
            cb.Fill();

            cb.RestoreState();
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            using (var pdfDoc = new Document(PageSize.A4))
            {
                var pdfWriter = PdfWriter.GetInstance(pdfDoc, new FileStream("Test.pdf", FileMode.Create));
                pdfDoc.Open();

                var table1 = new PdfPTable(1);
                table1.HeaderRows = 2;
                table1.FooterRows = 1;

                //header row  
                var headerCell = new PdfPCell(new Phrase("header"))
                {
                    HorizontalAlignment = Element.ALIGN_CENTER,
                    Border = 0
                };
                headerCell.CellEvent = new GradientCellEvent();
                table1.AddCell(headerCell);

                //footer row  
                var footerCell = new PdfPCell(new Phrase("footer"))
                {
                    HorizontalAlignment = Element.ALIGN_CENTER,
                    Border = 0
                };
                footerCell.CellEvent = new GradientCellEvent();
                table1.AddCell(footerCell);

                //adding some rows  
                for (int i = 0; i < 70; i++)
                {
                    var rowCell = new PdfPCell(new Phrase("Row " + i)) { BorderColor = BaseColor.LIGHT_GRAY };
                    table1.AddCell(rowCell);
                }

                pdfDoc.Add(table1);
            }

            //open the final file with adobe reader for instance.  
            Process.Start("Test.pdf");
        }
    }
}