[C#]Farbcode in einem Pixel

[...]
using System.Threading;

namespace WindowsFormsApplication41
{
    public partial class Form1 : Form
    {
        public int Yreihe = 0;

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            //Thread.Sleep(4000);
            Bitmap bmp = new Bitmap(System.Windows.Forms.Screen.PrimaryScreen.Bounds.Width,
                                    System.Windows.Forms.Screen.PrimaryScreen.Bounds.Height);
            Yreihe = MousePosition.Y;

            for (int i = 400; i < 900; i++)
            {
                Color pixelColor = bmp.GetPixel(i, Yreihe);
                if (pixelColor.ToString() != "Color [A=0, R=0, G=0, B=0]")
                {
                    MessageBox.Show(pixelColor.ToString());
                }
            }
        }
    }
}

  using System.Runtime.InteropServices;

  sealed class Win32
  {
      [DllImport("user32.dll")]
      static extern IntPtr GetDC(IntPtr hwnd);

      [DllImport("user32.dll")]
      static extern Int32 ReleaseDC(IntPtr hwnd, IntPtr hdc);

      [DllImport("gdi32.dll")]
      static extern uint GetPixel(IntPtr hdc, int nXPos, int nYPos);

      static public System.Drawing.Color GetPixelColor(int x, int y)
      {
       IntPtr hdc = GetDC(IntPtr.Zero);
       uint pixel = GetPixel(hdc, x, y);
       ReleaseDC(IntPtr.Zero, hdc);
       Color color = Color.FromArgb((int)(pixel & 0x000000FF),
                    (int)(pixel & 0x0000FF00) >> 8,
                    (int)(pixel & 0x00FF0000) >> 16);
       return color;
      }