Use LinearGradientBrush to draw a Rectangle : Gradient : Graphics C# Source Code

    

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.Drawing.Drawing2D;

public class Form1 : System.Windows.Forms.Form{
  private System.ComponentModel.Container components = null;

  public Form1(){
    InitializeComponent();
        SetStyle(ControlStyles.Opaque, true);
  }
  protected override void Dispose( bool disposing ){
    if( disposing ){
      if (components != null) 
      {
        components.Dispose();
      }
    }
    base.Dispose( disposing );
  }
    protected override void OnPaint(PaintEventArgs e) {
         Graphics g = e.Graphics;
         g.FillRectangle(Brushes.White, ClientRectangle);

         Brush linearGradientBrush = new LinearGradientBrush(
            new Rectangle(10, 60, 50, 50), Color.Blue, Color.White, 45);
         g.FillRectangle(linearGradientBrush, new Rectangle(10, 60, 50, 50));

         linearGradientBrush.Dispose();
         
    }
  private void InitializeComponent(){
    this.components = new System.ComponentModel.Container();
    this.Size = new System.Drawing.Size(300,300);
    this.Text = "Form1";
  }
  static void Main() {
    Application.Run(new Form1());
  }
}