Howto change only one special color in one Selection?

// Source bitmap
Aurigma.GraphicsMill.Bitmap bitmap = new Aurigma.GraphicsMill.Bitmap(@"c:/Rgb24.jpg");
Aurigma.GraphicsMill.BitmapData bitmapData = bitmap.LockBits(100, 100, 100, 100);

try
{
	// Apply channel balance
	Aurigma.GraphicsMill.Transforms.ChannelBalance transform = new Aurigma.GraphicsMill.Transforms.ChannelBalance();
	transform.Levels = new float[] {0.0f, 0.0f, -0.5f};
	transform.ApplyTransform(bitmapData);
}
finally
{
	bitmap.UnlockBits(bitmapData);
}

// Save results
bitmap.Save(@"c:\1.jpg");

// Source bitmap
Aurigma.GraphicsMill.Bitmap bitmap = new Aurigma.GraphicsMill.Bitmap(@"c:/Rgb24.jpg");
Aurigma.GraphicsMill.BitmapData bitmapData = bitmap.LockBits(100, 100, 100, 100);

try
{
	// Increase values of the second channel
	unsafe
	{
		int stride = bitmapData.Stride;
		byte *values = (byte *)bitmapData.Scan0.ToPointer();

		for(int i = 0; i < bitmapData.Height; i++)
		{
			byte *scanline = values + i * stride;

			for(int j = 0; j < bitmapData.Width; j++)
			{
				int channel = scanline[2];

				channel += 127;
				if(channel > 255)
					channel = 255;

				scanline[2] = (byte)channel;

				scanline += bitmapData.BitsPerPixel / 8;
			}
		}
	}
}
finally
{
	bitmap.UnlockBits(bitmapData);
}

// Save result
bitmap.Save(@"c:\2.jpg");