Problem z Mandelbrot (zielony)

Jak ktoś moze to prosze o pomoc bo nie wiem gdzie błąd roie!

/*
 * Created by SharpDevelop.
 * User: le
 * Date: 2008-12-03
 * Time: 20:53
 * 
 * To change this template use Tools | Options | Coding | Edit Standard Headers.
 */

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

namespace Le
{
	/// <summary>
	/// Description of MainForm.
	/// </summary>
	public partial class MainForm : Form
	{
		[STAThread]
		public static void Main(string[] args)
		{
			Application.EnableVisualStyles();
			Application.SetCompatibleTextRenderingDefault(false);
			Application.Run(new MainForm());
		}
		
		public MainForm()
		{
			//
			// The InitializeComponent() call is required for Windows Forms designer support.
			//
			InitializeComponent();
			
			//
			// TODO: Add constructor code after the InitializeComponent() call.
			//
		}
		
		void MainFormLoad(object sender, EventArgs e)
		{
			
		}
		
		void RysujClick(object sender, EventArgs e)
		{
			
			int maxX=ekran.Width;     //Wielkość ekranu do wyświetlania 
			int maxY=ekran.Height;
			int i,j, kolor;
			double amax,amin,bmax,bmin;
			amax=double.Parse(Amax.Text);
			amin=double.Parse(Amin.Text);
			bmax=double.Parse(Bmax.Text);
			bmin=double.Parse(Bmin.Text);
			double a,b;

			ekran.Image = new Bitmap(ekran.Width, ekran.Height);
			Graphics graph = Graphics.FromImage(ekran.Image);
			graph.FillRectangle(new SolidBrush(Color.White), 0, 0, ekran.Width, ekran.Height);
			
			for(i=0;i<maxX;i++)
			{
				a=(amax-amin)/maxX*i+amin;	
				for(j=0;j<maxY;++j)
				{
					b=-(bmax-bmin)/maxY*j+bmax;
					kolor=kolor_mandelbrota(a,b);
					graph.DrawRectangle(new Pen(Color.FromArgb(kolor,255,255)), i, j, 1,1);
//ekran(i,j,kolor);
				}
			}
		}
			 public int kolor_mandelbrota(double a, double b){
				
				int i, imax=100;
				double x,xx,y;
				double r,rmax=2;
				int kolor;
				x=y=0;
				for(i=0;i<imax;i++)
				{
					xx=(x*x)-(y*y)+a;
					y=((2*x)*y)+b;
					x=xx;
					r=Math.Sqrt((x*x)+(y*y));
					if(r<rmax)
						break;
				
					if(i==imax)
						kolor=255;
						
					else{
			        kolor=0;
			        					
					}
		return kolor;
				}
				
		}
		
	}
}

albo powiedzcie jak zrobic program podobny