PNG displayed incorrectly?

Question

I've created small project for studying purpose using C#, to read PNG resource in a .dll assembly.
Firstyly, I created a PNGResource.dll project embedded with "LargeIcon.png" and "SmallIcon.png". Access Modifier set to "Public".

Next, I created .exe project with a function like:

 private static System.Drawing.Image ReadBitmapFromResource(string ResName, Assembly ResAssembly)
{
    string ResFileName;
    if (ResAssembly.FullName.IndexOf(',') > 0)
    {
        ResFileName = string.Format("{0}.Properties.Resources.resources", ResAssembly.FullName.Substring(0, ResAssembly.FullName.IndexOf(',')));
    }
    else
    {
        ResFileName = string.Format("{0}.Properties.Resources.resources", ResAssembly.FullName);
    }
    using (ResourceReader ResReader = new ResourceReader(ResAssembly.GetManifestResourceStream(ResFileName)))
    {
        string ResType;
        byte[] ResByte;
        ResReader.GetResourceData(ResName, out ResType, out ResByte);
        if (ResType != null && ResByte != null ? ResType.IndexOf("System.Drawing.Bitmap") == 0 : false)
        {
            using (MemoryStream ResStream = new MemoryStream(ResByte))
            {
                 return (Image)(new BinaryFormatter().Deserialize(ResStream));
            }
        }
    }
    return null;
}

then in Form's OnLoad:

...
System.Reflection.Assembly assembly=System.Reflection.Assembly.LoadFrom("PNGResource.dll");

if (assembly != null)
{
 Image LargeIcon = ReadBitmapFromResource("LargeIcon", assembly);
 Image SmallIcon = ReadBitmapFromResource("SmallIcon", assembly);
}
... 

Those images are successfully displayed, but with a slight incorrectly visual: transparent pixels displayed as white pixels. I've ensured those PNGs have transparent pixels with Photoshop.
Something wrong with my code?