I'm using Reflector and can see some class names are black and others are light grey.
I tried doing a search for what this means and could not find a user guide or anything to indicate what this means.
I'm wondering if it might be related to the public/private of the class? I'm also assuming the envelope means sealed.
The black are public and the gray are not public (so they could be internal, private, etc.).
If you go to the Tools Menu -> Options and choose the Browser item, you can change the Visibility dropdown to show "Public Items Only". Then click Ok, all the gray items will be hidden.