HOW TO: Remove Colors Different From Shades of Specific Color - Keep only selected color and fill others with black - Winforms C#

Form ColorIndicator = null;

private void pickColorToolStripMenuItem_Click(object sender, EventArgs e)
{
   if (_viewer.Image == null)
   {
      MessageBox.Show("Unable to pick color! Please load an image first");
      return;
   }
   MessageBox.Show("Click a point on the image to select it. A small window will show the currently selected point when you move the mouse\n\nAfter selecting a point, verify the color using the Color dialog box");
   if (ColorIndicator == null)
   {
      ColorIndicator = new Form();
      ColorIndicator.TopMost = true;
      ColorIndicator.FormBorderStyle = System.Windows.Forms.FormBorderStyle.FixedSingle;
      ColorIndicator.MaximizeBox = false;
      ColorIndicator.MinimizeBox = false;
      ColorIndicator.Text = "Color indicator";
      ColorIndicator.Location = new Point(100, 100);
      ColorIndicator.Size = new System.Drawing.Size(200, 150);
   }
   ColorIndicator.Show();
   _viewer.MouseMove += _viewer_MouseMove;
   _viewer.MouseClick += _viewer_MouseClick;
}

// Convert mouse click to actual pixel coordinates
public Point ClientToBitmapPt(float x, float y)
{
   //Convert Client Coordinates to Bitmap Coordinates
   var t = _viewer.ImageTransform; //tems[0].Transform;
   Matrix m = new Matrix((float)t.M11, (float)t.M12, (float)t.M21, (float)t.M22, (float)t.OffsetX, (float)t.OffsetY);
   Transformer transformer = new Transformer(m);

   //Convert to compensate for view size mode, scale, scroll, etc...
   Point ptBmp = Point.Round(transformer.PointToLogical(new PointF(x, y)));

   // Put into LeadPoint
   LeadPoint leadPt = new LeadPoint(ptBmp.X, ptBmp.Y);

   //This is always a TopLeft, so convert to image view perspective
   leadPt = _viewer.Image.PointToImage(Leadtools.RasterViewPerspective.TopLeft, leadPt);

   // Put back into point
   ptBmp = new Point(leadPt.X, leadPt.Y);
   return ptBmp;
}

private void _viewer_MouseMove(object sender, MouseEventArgs e)
{
   var img = _viewer.Image;
   Point point = ClientToBitmapPt(e.X, e.Y);
   if (point.X >= img.Width || point.Y >= img.Height)
      return;
   var c = img.GetPixel(point.Y, point.X);
   ColorIndicator.BackColor = Color.FromArgb(c.R, c.G, c.B);
}

private void _viewer_MouseClick(object sender, MouseEventArgs e)
{
   ColorIndicator.Hide();
   _viewer.MouseClick -= _viewer_MouseClick;
   _viewer.MouseMove -= _viewer_MouseMove;
   Point point = ClientToBitmapPt(e.X, e.Y);
   var leadColor = _viewer.Image.GetPixel(point.Y, point.X);
   ColorDialog colorDialog = new ColorDialog();
   colorDialog.Color = Color.FromArgb(leadColor.R, leadColor.G, leadColor.B);
   colorDialog.AllowFullOpen = true;
   colorDialog.AnyColor= true;
   colorDialog.FullOpen = true;
   colorDialog.ShowDialog();
   leadColor = new RasterColor(colorDialog.Color.R, colorDialog.Color.G, colorDialog.Color.B);
   // Define upper and lower colors that conver the entire range of Saturation and Value, but limit Hue to values close to the selectec color.
   RasterHsvColor hsvLower = new RasterHsvColor(leadColor);
   RasterHsvColor hsvUpper = new RasterHsvColor(leadColor);
   hsvUpper.H = (byte)((hsvUpper.H + 25) % 255);
   hsvLower.H = (byte)((hsvLower.H - 25 + 255) % 255);
   hsvUpper.S = 255;
   hsvUpper.V = 255;
   hsvLower.S = 0;
   hsvLower.V = 0;
   // Define region for pixels that are NOT in the color range
   _viewer.Image.AddColorHsvRangeToRegion(hsvLower, hsvUpper, RasterRegionCombineMode.SetNot);
   // Fill the region with black
   FillCommand fill = new FillCommand(RasterColor.Black);
   fill.Run(_viewer.Image);

   _viewer.Image.MakeRegionEmpty();
}