Reading a certain pixels color from a window
You'll actually need to wrap the Bitmap in a using as well because its base class, Image, implements IDisposable:

public static Color GetPixel(IntPtr hwnd, int x, int y)
{
    using (Bitmap screenPixel = new Bitmap(1, 1);
    {
        using (Graphics gdest = Graphics.FromImage(screenPixel))
        {
            using (Graphics gsrc = Graphics.FromHwnd(MemoryHandler.GetMainWindowHandle()))
            {
                IntPtr hsrcdc = gsrc.GetHdc();
                IntPtr hdc = gdest.GetHdc();
                BitBlt(hdc, 0, 0, 1, 1, hsrcdc, x, y, (int)CopyPixelOperation.SourceCopy);
                gdest.ReleaseHdc();
                gsrc.ReleaseHdc();
            }
        }

        return screenPixel.GetPixel(0, 0);
    }
}


Further, the garbage collector works almost immediately. Or more simply put, if you use a memory allocation tool like MemProfiler, the memory will get cleaned up by GC faster than you can collect it with a snapshot. The Bitmap is likely where you are seeing the little tick.

It may also be worth wrapping the API call in a try ... finally:

IntPtr hsrcdc = gsrc.GetHdc();
IntPtr hdc = gdest.GetHdc();

try
{
    using (Graphics gsrc = Graphics.FromHwnd(MemoryHandler.GetMainWindowHandle()))
    {
        BitBlt(hdc, 0, 0, 1, 1, hsrcdc, x, y, (int)CopyPixelOperation.SourceCopy);
    }
}
finally
{
    gdest.ReleaseHdc();
    gsrc.ReleaseHdc();
}


to ensure the ReleaseHdc gets called.